3D IC method and device

ABSTRACT

A method of three-dimensionally integrating elements such as singulated die or wafers and an integrated structure having connected elements such as singulated dies or wafers. Either or both of the die and wafer may have semiconductor devices formed therein. A first element having a first contact structure is bonded to a second element having a second contact structure. First and second contact structures can be exposed at bonding and electrically interconnected as a result of the bonding. A via may be etched and filled after bonding to expose and form an electrical interconnect to interconnected first and second contact structures and provide electrical access to this interconnect from a surface. Alternatively, first and/or second contact structures are not exposed at bonding, and a via is etched and filled after bonding to electrically interconnect first and second contact structures and provide electrical access to interconnected first and second contact structure to a surface. Also, a device may be formed in a first substrate, the device being disposed in a device region of the first substrate and having a first contact structure. A via may be etched, or etched and filled, through the device region and into the first substrate before bonding and the first substrate thinned to expose the via, or filled via after bonding.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. application Ser. No. 14/198,723, filedMar. 6, 2014, which is a division of U.S. application Ser. No.13/783,553, filed Mar. 4, 2013, now U.S. Pat. No. 8,709,938, which is acontinuation of U.S. application Ser. No. 12/270,585, filed Nov. 13,2008, now U.S. Pat. No. 8,389,378, which is a continuation of U.S.application Ser. No. 11/201,321, filed Aug. 11, 2005, now U.S. Pat. No.7,485,968, the entire contents of each of which is incorporated hereinby reference.

This application is related to application Ser. No. 09/532,886, now U.S.Pat. No. 6,500,794, Ser. No. 10/011,432, now U.S. Pat. No. 7,126,212,Ser. No. 10/359,608, now U.S. Pat. No. 6,962,835, Ser. No. 10/688,910,now U.S. Pat. No. 6,867,073, and Ser. No. 10/440,099, now U.S. Pat. No.7,109,092.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of three-dimensionalintegrated circuits and more particularly to devices and the fabricationthereof of three-dimensional integrated circuits using direct waferbonding.

2. Description of the Related Art

Semiconductor integrated circuits (ICs) are typically fabricated intoand on the surface of a silicon wafer resulting in an IC area that mustincrease as the size of the IC increases. Continual improvement inreducing the size of transistors in ICs, commonly referred to as Moore'sLaw, has allowed a substantial increase in the number of transistors ina given IC area. However, in spite of this increased transistor density,many applications require an increase in total IC area due to a greaterincrease in required transistor count or an increase in the number oflateral interconnections required between transistors to achieve aspecific function. The realization of these applications in a single,large area IC die typically results in a reduction in chip yield and,correspondingly, increased IC cost.

Another trend in IC fabrication has been to increase the number ofdifferent types of circuits within a single IC, more commonly referredto as a System-on a-Chip (SoC). This fabrication typically requires anincrease in the number of mask levels to make the different types ofcircuits. This increase in mask levels typically also results in areduction in yield, and correspondingly, increased IC cost. A solutionto avoiding these undesired decreases in yield and increases in cost isto vertically stack and vertically interconnect ICs. These ICs can be ofdifferent size, come from different size wafers, comprise differentfunctions (i.e., analog, digital, optical), be made of differentmaterials (i.e., silicon, GaAs, InP, etc.). The ICs can be tested beforestacking to allow Known Good Die (KGD) to be combined to improve yield.The economic success of this vertical stacking and vertical interconnectapproach depends on the yield and cost of the stacking andinterconnection being favorable compared to the yield and costassociated with the increased IC or SoC area. A manufacturable methodfor realizing this approach is to vertically stack ICs using directbonding and to form vertical interconnect structures using conventionalwafer fabrication techniques including wafer thinning, photolithographymasking, via etching, and interconnect metallization. The verticalelectrical interconnection between stacked ICs can be formed as a directresult of the direct bonded stacking or as a result of a sequence ofwafer fabrication techniques after direct bonded stacking.

The cost of the vertical interconnection portion of this approach isdirectly related to the number of photolithography masking levelsrequired to etch vias and form electrical interconnects. It is thusdesirable to minimize the number of photolithography masking levelsrequired to form the vertical interconnection.

One version of vertical stacking and vertical interconnection is whereICs (on a substrate) are bonded face-to-face, or IC-side to IC-side.This version may be done in a wafer-to-wafer format, but is typicallypreferably done in a die-to-wafer format where die are bonded IC-sidedown, to a wafer IC-side up to allow the stacking of Known Good Die toimprove yield. The vertical interconnection may be formed as a directresult of the stacking, for example as described in application Ser. No.10/359,608, or as a result of a sequence of wafer fabrication techniquesafter direct bonded stacking. The sequence of wafer fabricationtechniques after direct bonded stacking typically includes thefollowing. The die are typically substantially thinned by removing mostof the die substrate. The die substrate can not, in general, be totallyremoved due to the location of transistors in the substrate, as is thecase, for example in bulk CMOS ICs. The substrate is thus typicallyremoved to the greatest extent practicable, leaving sufficient residualsubstrate to avoid damage to the transistors. An interconnection to thedie IC is then formed by etching a via through the remaining substrateto an interconnection location in the die IC, such that there are nonecessary transistors in the vicinity of this via. It is furthermorepreferable, in order to achieve the highest interconnection density, tocontinue this via through the entire die-IC and into the wafer-IC to aninterconnection location in the wafer IC. This via typically extendsthrough an insulating dielectric material that provides desiredelectrical isolation from interconnection locations in the die IC andwafer IC and exposes desired electrical connection locations in the dieIC and wafer IC. After the formation of this via, a verticalinterconnection can be made with a conductive material to exposeddesired electrical connection locations in the die IC and wafer IC. Aninsulating layer between the conductive material and the exposedsubstrate on the via sidewall may be used to avoid undesired electricalconduction between the conductive material and the substrate.

The fabrication of this structure typically takes four photolithographymasking levels to build. These levels are 1) via etch through substrate,2) via etch through insulating dielectric material in the die IC andwafer IC that exposes desired conductive material in the die IC andwafer IC, 3) via etch through a subsequently deposited insulating layerthat electrically isolates the conductive material that interconnectsthe interconnect location in the die IC with the interconnect locationin the wafer IC to the exposed substrate via sidewall that exposesdesired conductive material in the die IC and wafer IC, 4)interconnection with conductive material between exposed interconnectionpoint in the die IC with exposed interconnection point in the wafer IC.

The patterns defining the via etching through the insulating(dielectric) material(s) are typically smaller than the pattern definingthe via etch through the substrate to adequately expose theinterconnection points in the die IC and wafer IC and to avoid removinginsulating material on the substrate via sidewall. Since these patternsare formed after the via in the substrate, this patterning is typicallydone at a lower topographical level that the patterning of the substratevia. This results in a patterning over a non-planar structure thatlimits the scaling of the structure to very small feature size that isdesirable to achieve the highest interconnection density and consumesthe least possible silicon substrate where functional transistors wouldotherwise reside.

It is thus desirable to have a device that comprises a structure and amethod to fabricate said structure requiring a reduced number of maskingsteps and masking steps that can be realized on a planar surface, at thehighest, or one of the highest, levels of topography in the structure.It is further desirable to have a device that comprises a structure anda method to fabricate said structure whereby a minimum consumption ofsilicon where functional transistors would otherwise reside is achieved.

SUMMARY OF THE INVENTION

The present invention is directed to a method of three-dimensionaldevice integration and a three-dimensionally integrated device.

In one example of the method, a first element having a first contactstructure is integrated with a second element having a second contactstructure. The method may include the steps of forming a via in thefirst element exposed to at least the first contact structure, forming aconductive material in the via and connected to at least the firstcontact structure, and bonding the first element to the second elementsuch that one of the first contact structure and the conductive materialis directly connected to the second contact structure.

In a second example the method may include the steps of forming a via ina first element, forming a first conductive material in the via,connecting the first conductive material to the first contact structure,and bonding the first element to the second element such that one of thefirst contact structure and the first conductive material is directlyconnected to the second contact structure.

In a third example, the method includes the steps of forming a via in afirst element having a first substrate, forming a conductive material inthe via, forming a contact structure in the first element electricallyconnected to the conductive material after forming the via and theconductive material, forming a second element having at least one secondcontact structure, removing a portion of the first substrate to exposethe via and the conductive material, bonding the first substrate to thesecond substrate, and forming a connection between the second contactstructure and one of the first contact structure and the conductivematerial as a part of the bonding step.

In one example of an integrated structure according to the invention, afirst element has a first contact structure, a second element has asecond contact structure, a first via is formed in the first element, afirst conductive material is formed in the first via connected to thefirst contact structure, and the first element is bonded to the secondelement such that one of the first conductive material and the firstcontact structure is directly connected to the second contact structure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a diagram showing die to be bonded face-down to a waferface-up;

FIG. 2A is a diagram of die bonded to a substrate;

FIG. 2B is a diagram of die bonded to a substrate with a portion of thesubstrate of the die removed;

FIG. 2C is a diagram of a substrate bonded to another substrate;

FIG. 3A is a diagram showing formation of a dielectric film and masklayer over the structure of FIG. 2A;

FIG. 3B is a diagram showing formation a dielectric film and mask layerafter forming a planarizing material;

FIG. 4 is a diagram showing apertures formed in the dielectric film andmask layer of FIGS. 3A and 3B;

FIG. 5 is a diagram showing etching of the die using the aperture formedas shown in FIG. 4;

FIG. 6A is a diagram showing further etching to expose contactstructures in the die and wafer;

FIG. 6B is a diagram of a process modification including forming a hardmask;

FIG. 7A is a diagram of a section of the structure of FIG. 6A afterformation of a conformal insulative sidewall layer;

FIG. 7B is a variation of the embodiment where the hard mask is removed;

FIG. 8A is a diagram showing anisotropic etching of a conformalinsulative sidewall layer;

FIG. 8B is a variation of the embodiment where the hard mask is removed;

FIGS. 8C-8F illustrate variations in forming a conformal film in thebonded structure;

FIGS. 8G-8J illustrate the structures shown in FIGS. 8C-8J after etchingthe conformal film, respectively;

FIG. 8K illustrates an alternative manner of forming a sidewall film inthe bond structure;

FIG. 9A is a diagram showing forming a metal contact comprising a metalseed layer and a metal fill;

FIG. 9B is a variation of the embodiment where the hard mask is removed;

FIG. 9C is a variation of the embodiment where no seed layer is formed;

FIG. 10A is a diagram of the structure of FIG. 9A or 9B afterchemo-mechanical polishing;

FIG. 10B is a diagram of the structure of FIG. 9C after chemo-mechanicalpolishing;

FIGS. 10C-10F are diagrams illustrating alternative methods of filling acavity in the bonded structure;

FIG. 11 is a diagram illustrating metallization of the structure of FIG.10A;

FIG. 12 is a diagram of a second embodiment using a mask layer withoutan intervening dielectric layer;

FIG. 13 is a diagram showing forming a metal contact in the secondembodiment;

FIG. 14 is a diagram showing the structure of FIG. 13 afterchemo-mechanical polishing;

FIG. 15 is a diagram illustrating another embodiment of the invention;

FIG. 16A is a diagram illustrating an embodiment where a contactstructure is located in the surface of one of the devices;

FIG. 16B is a diagram of the structure of FIG. 16A after furtherprocessing;

FIG. 17 is a diagram showing a device produced using the methodaccording to the invention with the structure shown in FIGS. 16A and16B;

FIG. 18 is a diagram of another embodiment of the invention;

FIG. 19A is a diagram showing a device produced using the methodaccording to the invention with the structure shown in FIG. 18;

FIG. 19B illustrates the structure having a planarized material andcontact formed over the structure of FIG. 19A;

FIG. 19C illustrates directly bonded contacts similar to the structureof FIG. 19A but without an aperture;

FIGS. 20A-20H illustrate a fifth embodiment with sidewall films;

FIGS. 21A-21E illustrate a sixth embodiment where the substrate issubstantially completely removed;

FIGS. 22A-22L illustrate a seventh embodiment of where vias are formedprior to die singulation;

FIGS. 23A-23K illustrate an eighth embodiment die are mounted top down;

FIG. 23L illustrates bonding a structure with a filled via in top-downand top-up configurations;

FIGS. 23M and 23N illustrate bonding a second level of die;

FIG. 23O illustrates wafer-to-wafer bonding;

FIGS. 24A and 24B illustrate a variation of the eighth embodiment wheredie are mounted top up;

FIGS. 25A-25F illustrate a ninth embodiment with filled vias prior tobonding; and

FIGS. 26A and 26B illustrate a tenth embodiment with filled vias andsurface contacts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, in particular FIG. 1, a first embodimentof the method according to the invention will be described. It is notedhere that the drawings are not drawn to scale but are drawn toillustrate the concepts of the invention.

Substrate 10 includes a device region 11 having contact structures 12.Substrate 10 may be made of a number of materials, such as semiconductormaterial or insulating material, depending on the desired application.Typically, substrate 10 is made of silicon or III-V materials. Contactstructures 12 are typically metal pads or interconnect structures makingcontact to device or circuit structures (not shown) formed in substrate10. Substrate 10 may also contain an integrated circuit to which thecontact structures 12 are connected, and substrate 10 may be a modulecontaining only contact structures. For example, substrate 10 may be amodule for interconnecting structures bonded to substrate 10, orbringing out connections for packaging or integration with other modulesor circuit structures on, for example, a printed circuit board. Themodule may be made of insulative materials such as quartz, ceramic, BeO,or AlN.

Positioned for bonding to substrate 10 on surface 13 are three separateddie 14-16. Each die has a substrate portion 19, a device region 18 andcontact structures 17. The die may be previously separated from anotherwafer by dicing, etc. Die 14-16 may be made of a number of materials,such as semiconductor materials, depending on the desired application.Typically, the substrate is made of silicon or III-V materials. Contactstructures 17 are typically metal pads or interconnect structures makingcontact to device or circuit structures formed in device region 18. Thesizes of contact structures 12 and 17 each may vary. The typical rangeof contact structure size is between 1 and 20 microns, but the sizes andrelative sizes may be outside this range depending upon alignmenttolerances, circuit design parameters or other factors. The sizes of thecontact structures are drawn to illustrate the inventive concepts areand are not meant to be limiting. Device region 18 may also contain anintegrated circuit to which the contact structures 17 are connected.Substantially all of substrate portion 19 may be removed, leaving alayer of devices, a circuit, or a circuit layer. Also, the substrates ofdies 14-16 may be thinned after bonding to a desired thickness.

Die 14-16 may be of the same technology as wafer 10, or of differenttechnology. Die 14-16 may each be the same or different devices ormaterials. Each of die 14-16 has conductive structures 17 formed in adevice region 18. Structures 17 are spaced apart to leave a gaptherebetween, or may be a single structure with an aperture which mayextend across the entire contact structure. In other words, the aperturemay be a hole in contact structure or may divide the contact structurein two. The size of the gap or aperture may be determined by thephotolithographic design rules for the particular technology beingbonded. For example, a minimum lateral width of contact structures 12and 17 may be required to subsequently form a reliable, low resistanceelectrical connection with interconnect metal.

An additional factor that determines the optimum size of the gap oraperture is a ratio of a distance given by the vertical separationbetween contact structures 17 and 12 plus the thickness of the contactstructure 17 to the size of the gap or aperture. This defines an aspectratio of a via that will subsequently be formed between contactstructures 17 and 12 to enable an electrical interconnection betweencontact structures 17 and 12. This vertical separation is typically 1-5microns, or less, for oxide to oxide direct bonding, as described inapplication Ser. No. 09/505,283, the contents of which are incorporatedherein by reference, or potentially zero for metal direct bonding, asdescribed in application Ser. No. 10/359,608, the contents of which areherein incorporated by reference. Furthermore, the contact structure 17thickness is typically 0.5 to 5 microns. With a typical desired viaaspect ratio of 0.5 to 5 depending on the process technology used, atypical range of the size of the gap is 0.3-20 microns for oxide tooxide bonding or ˜0.1-10 microns for metal direct bonding. The metaldirect bonding case is described below in the fourth embodiment.

Dies 14-16 are generally aligned with the contact structures 12 suchthat structures 17 and the gap or aperture are positioned overcorresponding contact structures 12. The size of contact structures 12is chosen to allow die 14-16 to be simply aligned with the gap betweencontact structures 17. This size depends on the alignment accuracy ofthe method used to place die 14-16 on substrate 10. Typical methodsusing commercially available production tools allow alignment accuraciesin the range of 1-10 microns, although future improvements in thesetools is likely to result in smaller alignment accuracies. The lateralextent of contact structures 17 exterior to the gap or aperture ispreferably at least a distance given by this alignment accuracy.

Although only one set of contact structures 17 is shown for each die14-16, it is understood that the lateral extent of contact structures 17is typically much smaller than the lateral extent of each die 14-16, sothat each die may have several or a very large number of contactstructures 17. For example, contact structures 17 may have a lateralextent in the range of 1-100 microns and die 14-16 may have a lateralextent in the range of 1-100 mm. A quantity of contact structures 17 indie 14-16 having an order of magnitude 104 and much higher is thuspractically realizable.

As shown in FIG. 2A, surface 20 of die 14 is bonded to surface 13 ofsubstrate 10. This may be accomplished by a number of methods, but ispreferably bonded at room temperature using a bonding method asdescribed in application Ser. No. 09/505,283, where bonds of a strengthin the range of 500-2000 mJ/m², i.e., chemical bonds are formed. Thebonding of die 14-16 to substrate 10 is illustrated in FIG. 2. Afterbonding the substrates of die 14-16 are thinned. Thinning is typicallyachieved by polishing, grinding, etching, or a combination of thesethree techniques to leave thinned substrate 21 or to completely removesubstrate portion 19. FIG. 2B illustrates the example where substrateportion 19 is completely or substantially completely removed. Also, thesubstrates of dies 14-16 may be thinned prior to bonding.

While three die are shown bonded to a single substrate 10 in FIG. 2A, itis also possible to bond a larger or smaller number of die to substrate10. Also, it is possible to bond another substrate of a size comparableto that of substrate 10, which is illustrated in FIG. 2C where asubstrate 22 having a device region 23 is bonded to wafer 10 such thatspaced apart conductive structures 24 are generally aligned withconductive structures 12. Substrate 22 may be thinned or removed priorto bonding to facilitate alignment. Substrate 22 may be thinned afterbonding, and substantially all of substrate 22 may be removed ifdesired. The procedures described in the following figures are alsoapplicable to the structures shown in FIGS. 2B and 2C, but separatedrawings are omitted for brevity.

As shown in FIG. 3A, a conformal dielectric film 30 is formed oversurface 13 of substrate 10 and dies 14-16. This film may be formed by,for example, CVD, PVD or PECVD and preferably consists of an oxide filmsuch as silicon oxide of typical thickness range 0.1 to 1.0 micron.Also, a filler material such as a deposited or spun-on oxide or polymer32 such as polyimide or benzocyclobutene may be formed over and/orbetween dies 14-16, as shown in FIG. 3B. Material 32 may be formed atvarious points in the process. FIG. 3B shows the example where material32 is formed prior to forming films 30 and 40. Filler, material may alsobe formed after forming the structure shown in FIG. 3A, after forminghard mask 40 (FIG. 4), or at various other points in the processdepending on many factors such as the materials chosen or temperatureconsiderations. Other techniques may be used for forming fillermaterial. For example a dielectric filler, for example, silicon oxide,may be used by successive or iterative steps of dielectric formation,for example using methods described above, and chemical-mechanicalpolishing. Alternatively, a conductive filler, for example metal formedby, for example, electroplating, may be used by successive or iterativesteps of metal formation and chemo-mechanical polishing. Having a flatsurface may improve forming photoresist and other films on the surfaceand forming apertures in such films, for example, aperture 41 shown inFIG. 4.

Subsequently, a hard mask 40 is formed on dielectric film 30 andpatterned to leave apertures 41 generally aligned with structures 17(FIG. 4). The hard mask is preferably comprised of a material that has ahigh etch selectivity to a subsequent etch process or processes used toetch a via through thinned substrate 21 and device regions 18 and 11 tocontact structures 12. Examples of a hard mask are aluminum, tungsten,platinum, nickel, and molybdenum, and an example of an etch process isan SF₆-based reactive ion etch to etch a via through a thinned siliconsubstrate and a CF₄-based reactive ion etch to etch a subsequent viathrough device regions 18 and 11 to contact structures 12. The thicknessof the hard mask 40 is typically 0.1 to 1.0 microns. The width ofaperture 40 is dependent on a number of factors including the thicknessof thinned substrate 21 and the gap between contact structures 17, butis typically 1 to 10 microns.

Aperture 41 is formed using standard photolithographic patterning andetching techniques of the hard mask 40 and dielectric film 30. Forexample, an aperture can be formed in photoresist usingphotolithography. This aperture can be aligned to alignment marks on thedie 14-16 (or substrate 22), or substrate 10. Optical or IR imaging canbe used for the alignment. The hard mask 40 can then be etched with anappropriate wet chemical solution or a dry reactive ion etch processthat depends on the hard mask material, revealing the dielectric film 30in the aperture. The dielectric film 30 can then be etched in a mannersimilar to the hard mask 40 with an appropriate wet chemical solution ora dry reactive ion etch that depends on the dielectric film material. Anexample of a wet chemical solution for a hard mask is Aluminum EtchantType A if the hard mask is Aluminum. An example of a reactive ion etchprocess for a dielectric film material is a CF₄-based reactive ion etchif the dielectric film material is silicon oxide. Many other wet and dryetches are possible for these and other hard mask and dielectric filmmaterials. The width of the apertures 41 is preferably wider than thespacing between the structures 17 if the aperture is aligned to the die14-16 (or substrate 22), or, preferably wider than the spacing betweenthe structures 17 plus the alignment accuracy of the method used toplace die 14-16 (or substrate 22), on substrate 20 if the aperture isaligned to the lower substrate 20.

Using the hard mask 40, substrate portions of dies 14-16 are etched toform vias 50, as shown in FIG. 5. The etching is continued through thematerial adjacent to contact structures 12 and 17, which typically is adielectric material, to expose back and side portions of conductivestructure 17 and a top surface of contact structures 12. A first set ofgases and conditions, for example SF₆-based, may be used to etch throughthe substrate material of dies 14-16, and a second set of gases andconditions, for example CF₄-based, may be used to etch through thedielectric layers surrounding the contact structures 17. Both etches maybe performed in one chamber by switching gases and conditionsappropriately, without having to break vacuum. The etching to exposeconductive structure 12 is shown in FIG. 6A. The etching produces a viaportion 60 extending through the gap or aperture of contact structures17 to contact structure 12.

The dielectric via etching to expose contact structures 12 and 17preferably has a high etch selectivity to contact structures 17 so as toavoid a detrimental amount of etching to contact structures 17. However,there may be some combinations of dielectric via etching and conductivestructures that result in a detrimental amount of etching to contactstructures 17. For example, detrimental effects may occur whenconductive structure 17 is sufficiently thin or when the verticaldistance between contact structures 12 and 17 is sufficiently large.

An example of a detrimental amount of etching is some combinations ofaluminum contact structures 17 surrounded by silicon oxide dielectricand some CF₄-based reactive ion etches where the ratio of the aluminumconductive structure etch rate to the silicon oxide dielectric etch rateis comparable to or higher than the ratio of the thickness of contactstructure 17 to the thickness of silicon oxide dielectric betweencontact structures 12 and 17.

In those situations where there would be a detrimental amount of etchingto contact structures 17, the thickness of contact structures 17 may beincreased or an intermediate step is added to protect contact structures17 from the dielectric via etch. An intermediate process step can beused to avoid detrimental etching as follows. When the dielectricetching first exposes back and side portions of upper contact structure17, a hard mask, such as a metal material, can be selectively depositedon revealed portions of contact structure 17 before continuation of thedielectric etching results in detrimental etching to contact structure17. After selective deposition of a hard mask, the dielectric etchingcan be continued without detrimental etching to contact structure 17. Anexample of a selective deposition of a hard mask is electroless nickelplating. This is shown, for example, in FIG. 6B where etching is stoppedafter exposing contact structures 17 and before any significantdetrimental etching occurs. Contact structures 17 are then coated with aprotective hard mask material 61, for example, nickel using, forexample, electroless plating. A material such as nickel may remain inthe device in subsequent connecting of the contact structures 12 and 17.Alternatively, the material 61 may be removed before forming connectingstructures 12 and 17, if needed.

Note that protective hard mask 61 may also be selectively deposited onhard mask 40. An example is when hard mask 40 is conductive anddeposition of protective hard mask 61 is accomplished with electrolessplating. This may be advantageous for decreasing the required thicknessof hard mask 40. A further advantage of deposition of protective hardmask material 61 on hard mask 40 may be a restriction of the aperture ofvia 50 resulting in shadowing of a portion of contact structures 17 fromanisotropic etching of via 60. FIG. 7A illustrates one of the die 14-16in detail to more clearly illustrate the subsequent steps. A conformalinsulative film 70 is formed over mask 40 and contact structures 12 and17, and the sidewall of vias 50 and 60, partially filling vias 50 and60. Examples of a suitable insulative film are silicon oxide, siliconnitride or Parylene. The insulative film may be formed using a number oftypical deposition methods including but not limited to physical vapordeposition, chemical vapor deposition, and vapor phase deposition. Anexample of physical vapor deposition is sputtering, an example ofchemical vapor deposition is plasma enhanced chemical vapor deposition,and an example of vapor phase deposition is vaporization of a solid,followed by pyrolysis and then deposition.

Hard mask 40 or hard mask 40 and conformal dielectric film 30 may beremoved before formation of conformal insulative film 70 by, forexample, etching. FIG. 7B illustrates the case where hard mask 40 isremoved. If the etch to remove hard mask 40 or hard mask 40 and film 30is selective to materials exposed by vias 50 and 60, this etch can bedone without a mask. If this etch is not selective to materials exposedby vias 50 and 60, those materials subject to etch in vias 50 and 60 maybe masked with a suitable material. For example, if the hard mask 40,and contact structures 12 and 17 are all aluminum, the vias can bepartially filled with an easily removable spin-on viscous liquidmaterial to a depth such that contact structures 12 and 17 are covered.The vias can be partially filled with a spin-on viscous liquid materialby first selecting an adequate spin-on film thickness that will suitablyplanarize the surface formed by hard mask 40 through which vias 50 and60 were formed. Application of this film thickness will then result in amuch thicker film thickness inside the via than outside the via. Asuitable etch of the entire surface then removes this material from thesurface of hard mask 40 while leaving material in vias 50 and 60 thatcovers contact structures 12 and 17. An example of an easily removablespin-on material and suitable etch are photoresist and an O₂ plasmaetch, respectively.

Conformal film 70 is anisotropically etched to expose contact structures12 and 17 while leaving film 70 on the sidewalls of vias 50 and 60. Aback surface of structures 17 is preferably exposed to create a ledge 27for increasing the contact surface area, resulting in reduced contactresistance. A typical ledge 27 width in excess of 1 micron is preferredfor minimizing the contact resistance, but this distance will vary basedupon device and process parameters. FIGS. 8A and 8B depict the etchedconformal film 70, without and with mask 40 removed before formation ofconformal insulative film 70, respectively. Both of films 30 and 40 maybe removed prior to forming layer 70. In this case, following etching ofconformal layer 70 another insulating layer may be formed on substrateportion 21 (or device region 18 where portion 21 is completely removed)by oxidation or deposition, for example. Alternative to conformal film70, conformal films may also be formed before exposure of top surface ofcontact structure 12. For example, conformal film 71 may be formed afteretching through the substrate portions of die 14-16 but before etchinginto the material adjacent to contact structure 17, conformal film 72may be formed after etching into the material adjacent to contactstructure 17 but before reaching contact structure 17, conformal film 73may be formed after reaching contact structure 17 but before forming via60, or conformal film 74 may be formed after reaching conductivestructure 17 and forming part of via 60 but before completing via 60 andreaching contact structure 12 as shown in FIGS. 8C, 8D, 8E, and 8F,respectively. Conformal films 71, 72, 73, and 74 may subsequently beanisotropically etched to form isolating sidewalls on the via portion 50of the substrate portions of die 14-16. For example, conformal film 71may be subsequently anisotropically etched to form an isolating sidewallon the via portion 50 of the substrate portions of die 14-16, conformalfilm 72 may be subsequently anisotropically etched to form an isolatingsidewall on the via portion 50 of the substrate portion of die 14-16 andthe upper portion of via 50 comprised of material adjacent to contactstructure 17, conformal film 73 may be subsequently anisotropicallyetched to form an isolating sidewall on the entire depth of via 50, andconformal film 74 may be subsequently anisotropically etched to form anisolating sidewall on the entire depth of via 50 and the upper portionof via 60, as shown in FIGS. 8G, 8H, 8I, and 8J, respectively.

Alternative to the sidewall formed by the conformal deposition of films70, 71, 72, 73, or 74 and subsequent anisotropic etching of said films,a sidewall 75 can be formed selectively on the substrate portion of die14-16 in via 50, after said portion is formed by said via as shown inFIG. 8K. Sidewall 75 can be formed by a process that reactspreferentially to the substrate portion versus material adjacent tocontact structure 17. For example, if the substrate portion of die 14-16is silicon and the material adjacent to contact structure 17 is siliconoxide, a dielectric deposition process that nucleates preferentially onsilicon versus silicon oxide may be used, where the dielectricdeposition comprises sidewall 75, where sidewall 75 is structurallysimilar to conformal film 71 in via 50 after anisotropic etching ofconformal film 71 shown in FIG. 8K. Here, sidewall 75 is formed afteretching through the substrate portions of die 14-16 but before etchinginto the material adjacent to contact structure 17.

A side surface of contact structures 17 may also be exposed in theanisotropic etching to further increase the surface area and lower thecontact resistance. This is also shown in FIGS. 8A and 8B. The vias 50and 60 can then be further filled or completely filled with metal.Methods of filling vias 50 and 60 with metal include but are not limitedto physical vapor deposition (PVD), chemical vapor deposition (CVD) orelectroplating. Electroplating is typically used for the deposition ofthicker films than PVD or CVD and is typically preceded by thedeposition of a thin PVD or CVD seed layer. Examples of films formed byPVD are sputtered aluminum, palladium, titanium, tungsten,titanium-tungsten, or copper, examples of films formed by CVD aretungsten or copper, and examples of films formed by electroplating(which including electroless plating) are nickel, gold, palladium orcopper.

FIG. 9A shows an example of a masked electroplated method whereby ametal seed layer 90 is first deposited over the structure, makingelectrical contact to contact structures 12 and 17, followed byformation of a mask 91 using, for example, photoresist. Seed layer 90can be deposited by PVD, CVD, or electroplating as described above.Using mask 91 and electrical contact to seed layer 90, metal contact 92fills vias 50 and 60. In FIG. 9B, a structure is shown where mask 40 isremoved before formation of conformal insulative film 70, and FIG. 9Cshows the structure where no seed layer is used. A polishing step, forexample chemo-mechanical polishing, can then be used to remove theexcess portion of metal contact 92 outside of vias 50 and 60. Thispolishing step can also remove the metal seed layer 90 on the exposedside of die 14-16. It further can remove the hard mask 40 on the exposedside of die 14-16. The removal of hard mask 40 may be preferred if hardmask is electrically conductive as in the case of aluminum given above,in order to electrically isolate so formed metal filled vias from eachother. This polishing step may further remove conformal dielectric film30, resulting in a substantially planar surface and planar metalstructure 100 on the exposed side of die 14-16, as shown in FIGS. 10Aand 10B, where the structure in FIG. 10B is distinct from that in FIG.10A in that no seed layer is used prior to filling the via with metal.

Alternatively to filling vias 50 and 60 with metal followed by CMP, vias50 and 60 can be lined with metal 93, filled with dielectric 94 thenfollowed by CMP as shown in FIG. 10C. Vias 50 and 60 can be lined withmetal 93 by deposition using at least one of PVD, electroplating or CVD,as described above. Thickness of metal 93 is typically 0.01 to 0.2microns and may include a barrier layer adjacent to conformal insulativefilm 70 to prevent contamination of contact structures 12 or 17 ordevice regions 18 or 11. Examples of barrier layers include tantalumnitride, tungsten nitride, and titanium nitride and may be preceded by atitanium adhesion layer of typical thickness 0.005 to 0.02 microns. Atypical thickness of barrier layers is 0.005 to 0.05 microns. After aninitial thickness of 93 has been deposited, electroplating can also beused to conformally increase the thickness of 93 to a desired thickness.A typical increased thickness is 0.5 to 2.0 microns for via 50, subjectto via 50 of sufficient width. An example of dielectric 94 is siliconoxide and an example of filling is with plasma enhanced chemical vapordeposition (PECVD). This alternative has the advantages of reduced metaldeposition and metal CMP and the potential for a better coefficient ofthermal expansion′(CTE) match between the composite metal lined,dielectric filled via and the surrounding substrate portion of die14-16.

Another alternative to filling vias 50 and 60 with metal or lining vias50 and 60 with metal 93 followed by filling with dielectric 94 is tofill or line via 60 with metal 97 to form an electrical interconnectionbetween contact structures 12 and 17 without contacting thinnedsubstrate 21, and then fill vias 50 and 60 with dielectric 98, followedby CMP as described above and shown in FIG. 10D. Metal 97 can be formedto interconnect contact structures 12 and 17 without contacting thinnedsubstrate 21 by electroless plating that plates preferentially oncontact structures 12 and 17 by plating to sufficient thickness thatpreferential plating interconnects contact structures 12 and 17. Anexample of electroless plating that can be plated to sufficientthickness is nickel electroless plating. This alternative has theadvantage of not requiring a sidewall 60, 71, 72, 73, 74, or 75 on thevia 50 portion of remaining substrate die 14-16 to electrically isolatesaid electrical interconnection from said remaining substrate die asshown in FIG. 10D.

Electrical interconnection to interconnected contact structures 12 and17 can be formed by etching a via 51 through dielectric 98 to metal 97and filling via 51 with metal 46 as shown in 10E and similar to thedescription in FIG. 10B or by lining via 51 with conductive material 52and filling with dielectric 53 as shown in FIG. 10F and similar to thedescription in FIG. 10C. Via 51 in FIG. 10E and FIG. 10F is shownconnecting to the portion of metal 97 on contact structure 12.Alternatively, via 51 can connect the portion of metal 97 on contact 17or both contact structures 12 and 17.

The structures of FIGS. 10A-10F are suitable for subsequent processingincluding but not limited to photolithography-based interconnect routingor underbump metallization to support wirebonding or flip-chippackaging. This processing typically includes the formation of anelectrically insulating material on the exposed thinned substrate side21 to provide electrical isolation for the interconnect routing orunderbump metallization.

An example is shown in FIG. 11 with insulating material 96, such as adeposited or spun-on oxide or polymer, formed on the die 14-16 afterCMP, and interconnect routing or underbump metallization 95 formed onmaterial 96 in contact with metal structure 100. Another filler materialmay be used between die 14-16, as shown in FIG. 3B, prior to formingmaterial 96. Metallization may include several levels, separated byinsulating layers, not shown here, to accommodate a high via densityand/or a high degree of routing complexity. Alternatively, if thepolishing step does not remove conformal dielectric film 70, conformaldielectric film remains and may provide adequate electrical isolationfor the metallization structures.

A second embodiment of the method according to the invention isillustrated in FIG. 12. A hard mask 101 is formed on die 14-16 withoutany intervening dielectric layer. A typical range of hard mask 101thickness is 0.1 to 1.0 microns. The hard mask 101 is preferablycomprised of a material that has a high etch selectivity to a subsequentetch process or processes used to etch a via through thinned substrate21 and device regions 18 and 11 to contact structures 12. An example ofa hard mask is aluminum, tungsten, platinum, nickel, or molybdenum andan example of an etch process is an SF₆-based reactive ion etch to etcha via through a thinned silicon substrate and a CF₄-based reactive ionetch to etch a subsequent via through device regions 18 and 11 tocontact structures 12. Apertures 102 are formed in mask 101 and thestructure is processed as in the first embodiment to etch through thedie substrates and device regions to expose structures 12 and 17, whilepreferably exposing the top surface of structures 17 to form a ledge(such as 27 shown in FIGS. 8A and 8B). Metallization is carried out asshown in FIGS. 7-9 using mask 103 to form metal contact 104, to producethe structure shown in FIG. 13. After CMP (FIG. 14), metal 105 isplanarized, and the structure is suitable for subsequent processingincluding but not limited to photolithography-based interconnect routingor underbump metallization to support wirebonding or flip-chippackaging, similar to the metallization structure shown in FIG. 11. Thisprocessing may include the formation of an electrically insulatingmaterial on the exposed side of die 14-16 to provide electricalisolation for said interconnect routing or underbump metallization thatis routed over the exposed side of die 14-16. To further assistinterconnect routing or underbump metallization, a planarizing materialas described in the first embodiment, for example a dielectric or ametal, or alternatively, a polyimide or benzocyclobutene material may beformed to planarize the surface of the structure, for example by fillingany spaces between die, apertures or grooves, either before or after theCMP process.

The present invention may also be used with other structures. Forexample, a pair of contacts 17 is not required but a single contact in adie or wafer may be connected to a contact in the substrate to which itis bonded. This is illustrated in FIG. 15 where metal contact 107 toseed 90 interconnecting contact structures 12 and 108 with structure 108being offset from structure 12. One part (left side) of metal contact107 extends from the upper surface of substrate portion 109 directly toseed 90 on structure 108 while another part (right side) of metalcontact 107 extends from the upper surface of substrate portion 109directly to seed 90 on structure 12.

The present invention provides numerous advantages. A single mask isused to etch through the backside of a die or wafer bonded to asubstrate to interconnect the die or wafer and the substrate. Nophotolithography is needed in the via, which typically can becomplicated, problematic, and limit scaling. The etching proceedsthrough a bonding interface. Further, it is possible to expose topsurfaces of the contacts to be interconnected, increasing the surfacearea of the contact and reducing the resistance of the contact.Different technology devices can be interconnected, optimizing deviceperformance and avoiding the problems associated with trying tomanufacture different technologies with a single process sequence.

A third embodiment is shown in FIGS. 16A, 16B and 17. Substrate 110 hasdevice region 111 with contact structures 112. Die 114-116 each having adevice region 118, substrate portion 121 and contact structures 117 arebonded to substrate 110 on surface 113 as shown in FIG. 16A. In thisembodiment there is no material covering contact structures 112.Following the single masking process described for the first or secondembodiments, the structures shown in FIGS. 16B and 17 is produced. A via50 is etched through substrate portion 121 and device region 118,exposing a ledge 26 on the back surface of contact structures 117. Theetching is continued forming a via 60 and exposing a top surface ofcontact structure 112. Contact 120 is formed in the via, with or withouta seed layer 90, connecting contact structures 112 and 117. Fillermaterial may be used to planarize the device, as discussed above withrespect to FIG. 3B. Contact 120 may also be formed in the manner shownabove in FIGS. 10C-10F. Also, film 70 may be formed as shown in FIGS.8C-8K.

A fourth embodiment is shown in FIGS. 18-19. In this embodiment there isno material covering contact structures 122 or 123. Contact structures123 comprised of conductive material, for example metal, in die 114-116may extend above the surfaces of die 114-116 and contact structures 122comprised of conductive material, for example metal, may extend abovesurface 113. Contact structures 123 and contact structures 122 may becomposed of different metals. For example, contact structures 123 may becomprised of one copper, tungsten, nickel, or gold, and contactstructures 122 may be comprised of a different one of copper, tungsten,nickel, or gold. Contact structures 123 or contact structures 122 mayfurther be comprised of different metals, for example, a combination ofnickel, palladium, and gold. Contact structures 123 and contactstructures 122 may further be comprised of alloys of copper, tungsten,nickel, or gold or other alloys, for example indium-tin-oxide. Thesemetals may be formed by a variety of techniques including PVD, thermal,e-beam, and electroplating.

The portion of surfaces of die 114-116 excluding contact structures 123and the portion of surface 113 excluding contact structures 122 arepreferably a non-conductive material, for example silicon oxide, siliconnitride, silicon oxynitride, or an alternate isolating materialcompatible with semiconductor integrated circuit manufacturing. Die114-116 with exposed contact structures 123 are bonded to surface 113with exposed contact structures 122, as described in application Ser.No. 10/359,608, with an alignment accuracy sufficient to align a portionof exposed contact structures 123 in the surface of die 114-116 with aportion of exposed contact structures 122 in surface 113 and align thenon-conductive material portion of the surface of die 114-116 with a thenon-conductive material portion of surface 113. The bond between thenon-conductive material portion of surface of die 114-116 and thenon-conductive material portion of surface 113 is preferably a directbond as described in application Ser. No. 10/359,608. An alternate typeof direct bond, for example as described in application Ser. No.10/440,099 may also be used. The bond energy, preferably in excess of 1J/m², of the direct bond generates an internal pressure of contactstructures 122 against contact structures 123 that results in anelectrical connection between contact structures 122 and 123. It is thuspreferred to use a direct bond that results in a higher bond energy atlow temperature, for example those described above, in order to generatethe highest internal pressure; however, a direct bond that results in alower bond energy at low temperature, or requires a higher temperatureto obtain a higher bond energy may also be acceptable for someapplications. For example, a conventional direct bond that requiresmoderate temperature, for example less than 400EC, or moderate pressure,for example less than 10 kg/cm², to achieve a high bond energy, forexample greater than 1 J/m² may also be used.

Alternatively, contact structures 123 in die 114-116 may be nominallyplanar with the surfaces of die 114-116 and contact structures 122 maybe nominally planar with surface 113. Contact structures 122 and 123 mayhave a greater surface roughness than the non-metal surface portion ofdie 114-116 and non-metal portion of surface 113. For example, thesurfaces of die 114-116 and surface 113 preferably have aRoot-Mean-Squared (RMS) surface roughness less than 1 nm and furtherpreferably less than 0.5 nm, while the surfaces of contact structures122 and 123 preferably have a RMS surface roughness less than 2 nm andfurther preferably less than 1 nm.

The internal pressure of contact structures 122 against contactstructures 123 resulting from the bond between the non-contactstructures 123 portion of the surface of die 114-116 and the non-contactstructures 122 portion of surface 113 may not be adequate to achieve abond or result in an electrical connection with a preferably lowresistance due to, for example, a native oxide or other contamination,for example, hydrocarbons, on the exposed metal surface of die 114-116or surface 113. An improved bond or preferably lower resistanceelectrical connection between contact structures 123 and 122 may beachieved by removing the native oxide on contact structures 123 or 122.For example, dilute hydrofluoric acid may be used before contactingsurface 113 with die surfaces 114-116. Furthermore, surface 113 and thesurfaces of die 114-116 may be exposed to an inert ambient, for examplenitrogen or argon, after removing the native oxide until contactingsurface 113 with die surfaces 114-116. Alternatively, an improved bondor preferably lower resistance electrical connection between contactstructures 123 and 122 may be achieved after bonding non-contactstructures 123 portion of the surface of die 114-116 and the non-contactstructures 122 portion of surface 113 by increasing the temperature of,e.g. heating, contact structures 122 and 123. Temperature increase canresult in a preferably low resistance electrical connection by reductionof the native oxide or other contamination or by increasing the internalpressure between contact structures 123 and 122, for example if contactstructures 123 or 122 have a higher thermal expansion coefficientrelative to the non-metal material surrounding contact structures 123and 122, or by both reduction of native oxide or other contamination andincrease in internal pressure. The temperature increase may alsoincrease interdiffusion between contact structures, such as 122 and 123to result in a preferable low-resistance electrical connection. Thetemperature increase may thus enhance the metal bonding, metal contact,metal interconnect or conduction between contact structures 123 and 122.Contact resistances less than 1 ohm/:m² have been achieved. For example,for two contact structures of about a 5 and 10:m in diameter and eachabout 1:m thick, resistances less than 50 mohms have been obtained.

If there are ICs, for example silicon ICs, in die 114-116 or in layer111 below surface 113, the temperature increase is preferably less than400EC for 2 hours and further preferably less than 350EC for 2 hours toavoid damage to the ICs, contact structures or other metal structures.The temperature increase resulting in enhanced metal bonding, metalcontact, metal interconnect or conduction between contact structures 122and 123 may be very low, for example as low as 50EC for 10 minutes, ifcontact structures are comprised of a conductive material withsusceptibility to thermal expansion or internal pressure or negligiblenative oxide, for example, gold.

The use of contact structures 123 and 122 that result in a greaterincrease in internal pressure at lower post-bond temperature andfurthermore, are deformable at a lower pressure are preferred tominimize the post-bond temperature increase required to achieve thedesired enhancement in metal bonding, metal contact, metal interconnector conduction between contact structures 123 and 122, if required. Forexample, the internal pressure generated as a result of post-bondtemperature increase is dependent on the metal comprising contactstructures 123 and 122. For example, metals with high values ofCoefficient of Thermal Expansion (CTE), for example, copper, nickel, andgold, result in more expansion at a given temperature. Furthermore,metals with a higher shear modulus, for example tungsten and nickel,will generate more stress for a given expansion. Metals with a highproduct of CTE and shear modulus, for example copper, tungsten, andnickel, will thus be the most effective at generating an increase ininternal pressure with increased temperature. Furthermore, metals with alow yield stress, for example copper, nickel, and gold, preferably atvery high purity, for example over 99.9%, are more readily deformed atlower stress and can thus result in improved metal bonding, metalcontact, metal interconnect, and conductance between contact structuresat lower stress: Contact structures 123 and 122 comprised of metals witha high product of CTE and shear modulus, or high product of CTE andshear modulus normalized by yield stress, for example copper, nickel,and gold, are thus preferred for contact structures 123 and 122 thatexhibit improved metal bonding, metal contact, metal interconnect, andconductance between contact structures as a result of internal pressuregeneration with post-bond temperature increase.

Alternatively, contact structures 123 may be slightly below the surfacesof die 114-116 or contact structure 122 may be slightly below surface113. The distance below surfaces of die 114-116 and surface 113 ispreferably less than 20 nm and further preferably less than 10 nm.Subsequent bonding followed by temperature increase may increase theinternal pressure between contact structures 122 and 123 as describedabove and result in improved metal bonding, metal contact, metalinterconnect, or conductance between contact structures 122 and 123. Theslight distance of contact structures 122 below surface 113 and theslight distance of contact structures 123 below the surfaces of die114-116 is an average distance over the extent of the contactstructures. The topography of the contact structures will includelocations equal, above, and below the average distance. The total heightvariation of the contact structures, given by the difference between themaximum and minimum height, may be substantially greater than the RMSvariation. For example, a contact structure with a RMS of 1 nm may havea total height variation of 10 nm. Accordingly, although contactstructures 123 may be slightly below the surfaces of die 114-116 andcontact structures 122 may be slightly below the surface 113 asdescribed above, a portion of contact structures 122 may extend abovethe surfaces of die 114-116 and a portion of contact structures 123 mayextend above the surface 113, resulting in a mechanical connectionbetween contact structures 122 and contact structures 123 after bondingof the non-metal portion of surface 113 to non-metal portion of die114-116. This mechanical connection may not result in an adequateelectrical connection between contact structures 122 and contactstructures 123 due to an incomplete mechanical connection or nativeoxide or other contamination on contact structures 122 or contactstructures 123. Subsequent temperature increase may improve the metalbonding, metal contact, metal interconnect, conductance between contactstructures 122 and 123 as described above.

Alternatively, the temperature increase may result in mechanical contactand/or desired electrical interconnection between contact structures 123and 122 if the highest portion of contact structures 123 is below thesurface of die 114-116 or the highest portion of contact structures 122is below surface 113 and there is not a mechanical contact betweencontact structures 123 and 122 after bonding.

Alternatively, contact structures 123 may be below the surface of die114-116 and contact structures 122 may above surface 113, or contactstructures 123 may be above the surface of die 114-116 and contactstructures 122 may be below surface 113. The difference between thedistances of contact structure 122 below surface 113 and contactstructures 123 below the surface of die 114, 115, or 116 (or vice versa)can be slightly positive as described in application Ser. No.10/359,608. Alternatively, the difference between the distances ofcontact structure 122 below surface 113 and contact structures 123 belowthe surface of die 114, 115, or 116 (or vice versa) can be nominallyzero or slightly negative and a post-bond temperature increase mayimprove the metal bonding, metal contact, metal interconnect,conductance between contact structures 122 and 123 as described above.

The height of contact structures 123 relative to the surface of die114-116 and the height of contact structures 122 relative to the heightof surface 113 can be controlled with a polishing process that forms thesurfaces of die 114-116 or surface 113, for example chemo-mechanicalpolishing (CMP). The CMP process typically had a number of processvariables including but not limited to type of polishing slurry, rate ofslurry addition, polishing pad, polishing pad rotation rate, and polishpressure. The CMP process is further dependent on the specific non-metaland metal materials comprising surface 113 and the surface of die114-116, relative polishing rates of non-metal and metal materials(similar polishing rates are preferred, for example nickel and siliconoxide), size, pitch and grain structure of the contact structures 122and 123, and non-planarity of surface 113 or surface of die 114-116.Optimization of these process parameters can be used to control theheight of contact structures 123 relative to the surface of die 114-116and the height of contact structures 122 relative to the height ofsurface 113. Alternate polishing techniques, for example slurry-lesspolishing, may also be used.

The height of contact structures 123 relative to the surface if die114-116 and the height of contact structures 122 relative to the heightof surface 113 may also be controlled with a slight dry etch of thematerial around contact structures 123 on the surface of die 114-116 orthe material around contact structures 122 on surface 113, for example aplasma or reactive ion etch using mixture of CF₄ and O₂, for thesurfaces comprised of certain dielectric materials, for example siliconoxide, silicon nitride, or silicon oxynitride, preferably such that anincrease in surface roughness, that would significantly decrease thebond energy between said surfaces, results. Alternatively, the height ofcontact structures 123 and contact structures 122 may be controlled bythe formation of a very thin metal layer on contact structures 123 and122. For example, electroless plating of some metals, for example gold,can be self-limiting to a very thin layer, for example approximately5-50 nm. This method may have the additional advantage of terminating anoxidizing metal with very thin non-oxidizing metal, for example gold onnickel, to facilitate the formation of electrical connections.

Furthermore, contact structures 122 can have a lateral dimension largeror smaller than the lateral dimension of contact structures 123 suchthat after bonding, the perimeter of a contact structure 123 iscontained within contact structure 122 or the perimeter of a contactstructure 122 is contained within the perimeter of contact structure123. The minimum lateral dimension larger or smaller is typicallydetermined by at least twice the alignment accuracy of bonding die114-116 to surface 113. For example, if the alignment accuracy inbonding die 114-116 to surface is one micron, contact structures 122 arepreferably at least two microns larger than contact structures 123 inorder for the perimeter of contact structures 123 to be contained withinthe perimeter of contact structures 122.

The maximum internal pressure of contact structures 122 against contactstructures 123 that can be generated from the bond between the portionof the surface of die 114-116 around contact structures 123 and portionof surface 113 around contact structures 122 or accommodated bypost-bond temperature increase depends on the bond area of this portionof the surface of die 114-116 to this portion of surface 113 and thearea of contact structures 123 against the area of contact structures122. The sum of these two areas is typically less than the entire areaof die 114-116 against surface 113 due to a residual area of contactstructures 123 aligned with a non-contact structures 122 portion ofsurface 113 and a residual area of contact structures 122 aligned with anon-contact structures 123 portion of the surface of die 114-116 thatresults from a difference in lateral dimension between contactstructures 123 and 122 and a bond misalignment between the surfaces ofdie 114-116 and surface 113. The maximum internal pressure that can begenerated by bonding or accommodated by post-bond temperature increasecan be approximated by the fracture strength of the bond between theportion of the surface of die 114-116 and the portion of surface 113times the ratio of the area of this bond to the area of contactstructures 123 against the area of contact structures 122. For example,if the portion of the surfaces of die 114-116 and the portion of surface113 is comprised of silicon oxide with a fracture strength of 16,000 psiand the direct bond between the aligned portion of these portions has afracture strength about one half that of silicon oxide, or 8,000 psi,and the contact structures 123 and 122 are circular with a diameter of 4microns on a pitch of 10 microns, and perfectly aligned, a maximuminternal pressure between contact structures 123 and 122 in excess of60,000 psi is possible. This pressure is typically significantly greaterthan that generated by a post-bond temperature increase. For example, ifcontact structures 123 and 122 are comprised of copper with a CTE of 17ppm and a shear modulus of 6,400,000 psi and the portion of the surfaceof die 114-116 and the portion of surface 113 is comprised of siliconoxide with a CTE of 0.5, and contact structures 123 are planar with theportion of die 114-116 and contact structures 122 are planar with theportion of surface 113, a stress of approximately 37,000 psi betweencontact structures 123 and 122 is expected at a post-bond temperatureincrease of 350EC.

Contact structures 123 and 122 are typically not perfectly aligned andof the same lateral dimension. This may result in a portion of contactstructures 123 in contact with a portion of surface 113 around contactstructures 122 or a portion of contact structures 122 in contact with aportion of the surface of die 114-116 around structure 123. If a portionof contact structures 123 is in contact with this portion of surface 113and further, if contact structures 122 are below surface 113 or,alternatively, if a portion of contact structures 122 is in contact withthis portion of the surface of die 114-116 and further, if contactstructures 123 are below the surface of die 114-116, then post-bondtemperature increase can result in an increase of internal pressurepreferentially between contact structures 122 and this portion of thesurface of die 114-116 or contact structures 123 and this portion ofsurface 113, and result in a decrease in internal pressure at a givenpost-bond temperature increase between contact structures 123 and 122that would otherwise be obtained. To avoid this decrease in internalpressure increase between contact structures 123 and 122, it ispreferred that if contact structures 123 are below the surface of die114-116, the perimeter of contact structures 122 is within the perimeterof contact structures 123 after bonding by an amount to accommodatemisalignment and mismatch in size and shape of contact structures 123and contact structures 122 (such as twice the alignment tolerance) sothat internal pressure increase will be primarily between contactstructures 123 and contact structures 122. Alternatively, it ispreferred that if contact structures 122 are below surface 113, theperimeter of contact structures 123 is within the perimeter of contactstructures 122 after bonding by an amount to accommodate misalignmentand mismatch in size and shape of contact structures 123 and contactstructures 122 so that internal pressure increase will be primarilybetween contact structures 123 and contact structures 122. Furtheralternatively, if contact structures 123 are below the surfaces of die114-116 and contact structures 122 are below surface 113, the contactstructures least below the surface, normalized by the contact structuresCTE, has a perimeter within the perimeter of the opposing contactstructure after bonding by an amount to accommodate misalignment andmismatch in size and shape of contact structures 123 and contactstructures 122 so that internal pressure increase will be primarilybetween contact structures 123 and contact structures 122.

The temperature of contact structures 123 and contact structures 122 canbe increased before or after thinning the substrates of die 114-116 toform thinned die substrates 121. The temperature of contact structures123 and contact structures 122 can be increased after bonding with avariety of types of heating including but not limited to thermal,infrared, and inductive. Examples of thermal heating include oven, beltfurnace, and hot plate. An example of infrared heating is rapid thermalannealing. The infrared heating source can be filtered to preferentiallyheat contact structures 123 and 122 with photons of a preferred energy.For example, if substrate 110, die 114-116 substrate, thinned diesubstrate 121, device region 111, or device region 118 are comprised ofa semiconductor, for example silicon, the infrared heat source can befiltered to prevent photons with energy in excess of the semiconductorbandgap from being absorbed by the semiconductor, resulting in a reducedtemperature increase of the semiconductor compared to the temperatureincrease of contact structures 123 or contact structures 122. An exampleof inductive heating is inductive magnetic resonance when contactstructures 123 or contact structures 122 are magnetic, for examplecomprised of nickel.

A plurality of contact structures 123 may contact a single contactstructure 122 without covering the entirety of a single contactstructure 122 as shown in FIG. 18. Alternatively, a single contactstructure 123 may contact a single contact structure 122, eitherpartially or in its entirety, a single contact structure 122 may contacta single contact structure 123, either partially or in its entirety, ora single contact structure 123 may contact a plurality of contactstructures 122.

Following the single masking process described for the precedingembodiments, the structure shown in FIG. 19A may be produced when aplurality of contact structures 123 contacts a single contact structure122 without covering the entirety of a single contact structure 122,where metal seed layer 90 forms an electrical interconnection to bothcontact structures 122 and 123. Alternatively, metal seed layer 90 mayonly contact structures 123, particularly if contact structures 123cover the entirety of contact structures 122. The structure shown inFIG. 19A may be further processed to form a surface similar to surface113 in FIG. 18 as described earlier in this embodiment and shown in FIG.19B where contact structure 59 is similar to contact structure 122 andplanarized material 58 is similar to the non-contact 122 portion ofsurface 113. Additional die with exposed contact structures 123 may thenbe bonded and interconnected to the surface with exposed contact 59similar to the bonding of die 114-116 with exposed contact structures123 to exposed contact structure 122. FIG. 19C illustrates a filled viawith contact 124 without an aperture or gap.

In this fourth embodiment, a via etch followed by metal interconnectionis not needed to make an electrical interconnection between contactstructures 123 and 122. However, a via etch followed by metalinterconnection as shown in FIG. 19A may be desired to provide forelectrical access from the exposed side of die 114-116. An example of anapplication where this may be desired is in the flip-chip bump bondingof the exposed side of die 114-116 to a package, board, or integratedcircuit to make electrical connection between contact structures 123 or122 and this package, board, or integrated circuit. There are alsoapplications where a via is not required for this purpose, for examplein the fabrication of certain types of Staring Focal Plane Arrays. Forthese applications, the method and devices fabricated thereby as shownin FIG. 18 including, but not limited, to the derivations describedabove may suffice.

A fifth embodiment is shown in FIGS. 20A-20H. This embodiment is similarto the previous embodiments before the formation of via 50 with theexception that contact structures in die 17, 108, 117, or 123 with anaperture or edge that overlaps via 50 is replaced with contact structure87 without an aperture or overlapping edge. In this embodiment, contactstructures 87 in die 84-86 with substrate portion 89, device region 88are bonded to surface 83 with device region 81, substrate 80, andcontact structures 82. Contact structure 87 is positioned over contactstructure 82 as shown in FIG. 20A. Die 84-86 can also be bonded to asurface 113 with exposed contact structures 112 similar to that shown inFIGS. 16 and 17 or contact structures 122 similar to that shown in FIGS.18 and 19. Note that the contact structure 87 may be bonded in directcontact with contact structure 82, which is illustrated in device 86.Dies 84-86 may also have the same contact structure configuration. FIGS.20A and 20B are drawn to show two contact structure configurations, witha cutout between the two configurations for brevity. Typically each ofthe die bonded to a substrate will have the same contact structureconfiguration. If die with different contact structures are bonded tothe same substrate, certain process variations may be required such asadjusting etch parameters or etching vias separately. The figures aredrawn to illustrate the invention where either the same or differentstructures are present on a substrate, and do not necessarily show suchvariations.

Patterned hard mask 40 and aperture 41 are formed as described in thefirst embodiment and shown in FIG. 20B. Via 55 is then formed bysequentially anisotropically etching remaining substrate portions 89 indie 84-86, portion of device region 88 in die 84-86 to contact structure87, contact structure 87 creating side surface 79, remainder of deviceregion 88 to surface 83 (if needed), and device region 81 (if needed) tocontact structure 12. With the exception of etching contact structure87, these anisotropic etches may be done as described in the firstembodiment. Regarding the anisotropic etching of contact structure 87,an RIE etch that etches conductive structure 87 selective to hard mask40 may be used. If hard mask 40 and conductive structure 87 have similaretch rates, hard mask 40 may be formed substantially thicker thancontact structure 87 to cause exposed contact structure 87, along withsubstrate portion 89, device region 88, contact structure 87, and deviceregion 81 to contact structure 82 (as needed), to be etched withoutentirely etching hard mask 40. The etch for contact structure 87 may besubstantially different than the etch for the remaining substrateportion 89 and device region 88 in die 84-86 and device region 81. Forexample, if the remaining substrate portion 89 is comprised of silicon,and the etched portions of device regions 88 and 81 are comprised ofsilicon oxide, and contact structure 87 is comprised of Al, anon-chlorine-based RIE etch can be used to etch the remaining substrateportion 89 and device regions 88 and 81, and a chlorine-based RIE etchcan be used to etch contact structure 87.

The sidewall 76 is preferably formed before the etching of contactstructure 87. Specifically, the structure is anisotropically etchedthrough substrate portion 89 and can stop after reaching device region88, or continue into device region 88 while stopping short of contactstructure 87. Layer 76 is then formed, as shown in FIG. 20C for thesetwo cases, for separated contact structures and directly bonded contactstructures. Layer 76 may be formed by depositing an insulating layersuch as a silicon oxide in via 55 followed by removal of the layer fromthe bottom of via 55 by, for example, anisotropic etching. The remainderof device region 88 and contact structure 87 are etched through toexpose contact structure 82, as shown in FIG. 20D (left side) and theremainder of device region 88 is etched through to expose contact 87 inFIG. 20D (right side).

The subsequent steps of sidewall formation, electrical interconnectionbetween contact structures 82 and 87, and via lining and/or fillingfollows as described in the previously described embodiments with theprimary exception that the electrical interconnection to contactstructure 87 is limited to a side surface 79 exposed by anisotropicallyetching through contact structure 87. A second exception is sidewallformation similar to that shown by sidewall 70 in FIG. 8A or 8B, orsidewall 74 shown in FIG. 8J where the sidewall extends below contactstructure 17 and would inhibit an electrical interconnection to sidesurface 79 of contact structure 87. FIG. 20D (left side) illustrates oneof the die 84-86 in detail to more clearly illustrate an example of asidewall 76 not inhibiting an electrical interconnection to side surface79.

The example of sidewall formation in FIG. 20D is similar to thatpreviously given in FIG. 8H where the sidewall 72 extends below thinneddie substrate 21, but above contact structures 17. The etching of via 55through contact structure 87, or through the region between contactstructure 87 and contact structure 82 can also be slightly isotropicabove contact structure 87 to form a very small self-aligned ledge 28 onthe topside of contact structure 87 to reduce the interconnectresistance of the subsequently formed electrical interconnect betweencontact structures 82 and 87 without substantially increasing thecross-section of via 55, as shown in FIG. 20E. A selective sidewall 77similar to the sidewall 75 formed as shown in FIG. 8K can also be formedbefore etching of contact structure 87 (FIG. 20F, left or right side) orafter etching of contact structure 87 (FIG. 20F, left side). Theformation of a selective sidewall 77 after etching of contact structure87 overhangs exposed side surface 79 and can complicate formation of anelectrical interconnection between exposed side surface 79 and contactstructure 82. This complication can be avoided by the formation ofelectrical interconnection 99 between exposed side surface 79 andcontact structure 87 in a manner similar to the formation of electricalinterconnection 97 electrically interconnecting contact structures 12and 17 but not contacting thinned substrate 21 shown in FIG. 10D.Interconnect 99 can extend above contact structure 87 but below anyconductive material in 88 or 89.

Subsequent to electrical interconnection 99 formation, a sidewall 76covering substrate portion 89 exposed to via 55 similar to sidewall 70in FIG. 8A or 8B can be formed as shown in FIG. 20G where a sidewallthickness comparable to interconnect 99 thickness is assumed.Alternatively, a selective sidewall similar to sidewall 75 in FIG. 8Kcan be formed as shown in FIG. 20H. The remaining portion of via 55 canthen be filled with metal or lined with metal and filled with dielectricas described in previous embodiments.

These resulting structures are also suitable for subsequent processingincluding but not limited to photolithography-based interconnect routingor underbump metallization to support wirebonding or flip-chip packagingas described in previous embodiments. It is noted that the structuresshown in FIGS. 20C-20F may also include the contact structuresconfigured as shown in die 86.

A sixth embodiment is shown in FIGS. 21A-21E where the entire diesubstrate portion 127, or substantially all of portion 127, similar to19, 21, 89, 109, 121, in previous embodiments, may be removed leaving alayer of devices, a circuit, or a circuit layer. In this embodiment,substrate 130 has device region 131 with contact structures 132. Die134-136 each having a device region 138, contact structures 137, andsubstrate portion 127 not required for proper operation. Contact 137 isshown having an aperture in die 134, and contact 137 is unitary in die135 and an aperture may be etched therethrough, as in the fifthembodiment. Die 134-136 are bonded to substrate 130 on surface 133 asshown in FIG. 21A. Die substrate 127 is removed entirely by, forexample, grinding and/or polishing, exposing device region 138 as shownin FIG. 21B. The number of steps subsequently required to etch a via toexpose contact structures and form an electrical interconnection betweencontact structures is substantially reduced and simplified for thisembodiment compared to the previous embodiments due to the lack ofsubstrate portion 127.

For example, in FIG. 21C, where only one of the die 134-136 is shown,the step of etching a via 129 to expose contact structures 132 and 137is simplified because there is no substrate portion 127 through which avia is required to be etched. Via 129 can thus be substantially lessdeep than the vias described in earlier embodiments, resulting in asubstantial reduction in via cross section and corresponding increase invia density. In another example, in FIG. 21D, where only one of the die134-136 is shown, the step of forming an electrical interconnection 128between exposed contact structures 132 and 137 is simplified becausethere is no substrate portion 127 that requires a sidewall toelectrically isolate electrical interconnection 128. FIG. 21Eillustrates this embodiment including contact structures bonded indirect contact. It is noted that the structure shown in FIG. 21E mayalso include the contact structures configured as shown in die 135 andsimilar to contact structures 124 and 122 in FIG. 19C.

Examples of applications where the entire die substrate portion may beremoved include some silicon-on-insulator and III-V ICs where the diesubstrate portion of said ICs is not used for active transistor or otherIC device fabrication.

The structures resulting from the sixth embodiment are also suitable forsubsequent processing including but not limited tophotolithography-based interconnect routing or underbump metallizationto support wirebonding or flip-chip packaging as described in previousembodiments.

Other variations to those shown in FIGS. 21A-21E include, but are notlimited to, those described in earlier embodiments, for example; viafilling or via lining and filling as shown in FIG. 10 and FIG. 14;interconnection to a die contact structure edge as shown in FIG. 15;bonding die with wafer contact structures exposed as shown in FIG. 17and FIG. 18, or die and wafer contact structures exposed as shown inFIG. 19; Contact to an exposed side surface of die contact structures asshown in FIG. 20 is also possible.

A seventh embodiment of the invention is shown in FIGS. 22A-L and FIGS.23A-K. Note that the surface contact structure configuration isillustrated by die 146. All dies may have the same or different contactstructure configuration in a substrate and certain process variationsmay be needed when different contact structures are bonded to the samesubstrate, as discussed above. Substrate 140 may contain die such as144-146 (indicated by dashed lines) separated by scribe alleys 38. Eachof die 144-146 has contact structures 147 located in device region 148.It is noted that the contact structures are not drawn to scale, for easeof explanation. Contact structures 147 may be separate members or mayconsist of one member having an aperture therethrough.

Contact structures 147 can be formed by conventional methods of metaldeposition and liftoff or metal deposition and etch. Alternatively,contact structures 147 can be formed by patterning and etching through apre-existing conductive layer or a combination of patterning and metaldeposition within an aperture of a conductive layer. Formation ofcontact structures 147 is preferably followed by deposition of aplanarizing layer of electrically isolating dielectric material 151similar to that under contact structures 147 in device region 148. Atypical planarization material is silicon oxide formed by plasmaenhanced chemical vapor deposition as indicated by layer 151 in FIG.22A. When surface contacts are desired, as in device 146, layer 151 maybe not formed, not formed in certain areas of substrate 140, or may belater removed.

A via may be formed in dies 144-146. Etching of the via is preferablydone at wafer-scale, prior to singulation of die 144-146 along scribealleys 38, into individual die so that all vias on all die on a wafercan be etched simultaneously. Die 144-146 can thus have all their viasetched simultaneously, or alternatively, at separate times if die144-146 originate from different wafers. The vias are preferably etchedanisotropically to consume a minimum amount of device region material148 and substrate 140.

The contact structures in die 144-146 may also be formed in a mannersimilar to that described previously in the fifth embodiment. Forexample, planarization material 151 is patterned and etched to form avia 152 through planarization material 151 to conductive material 154 asshown in FIG. 22B, followed by etching a via through conductive material154 to form contact structures 147 (154) with an exposed side surface153, followed by further etching through device region 148 and intosubstrate 140 to form via 155 as shown in FIG. 22C. This etch ispreferably anisotropic to minimize the lateral extent of via 155.Planarization material 151 may also be patterned and etched to form vias156 exposing two ledges 160 as shown in FIG. 22D, vias 157 exposing oneledge 160 as shown in FIG. 22E, or vias 158 where no ledge is exposed asshown in FIG. 22F. The patterning and etching of planarization material151 may be of an area slightly larger than the aperture formed bycontact structures 147 (or in contact structures 154) resulting in alocation and lateral extent of vias 156 below contact structure 147given by contact structure 147 (154) and an upper portion of vias 156above contact structure 147 (154) slightly wider than the lower portionof vias 156. The ledges 160 and side surface 153 of contact structures147 (154) are revealed, as shown in FIG. 22D. Alternatively, thepatterning and etching of planarization material 151 may overlap an edgeof contact structures 147 (154) resulting in a portion of the locationand lateral extent of vias 157 given by contact structure 147 (154) andthe upper portion of via 157 slightly wider than the lower portion. Oneledge 160 of contact structure 147 and 154 and a side surface 153 ofcontact structures 147 (154) are revealed, as shown in FIG. 22E.Alternative to FIGS. 22D and 22E, the patterning and etching ofplanarization material 151 may not overlap any portion of contactstructures 147 (154) resulting in a location and lateral extent of via158 not given by contact structure 147 (154) and not revealing a sidesurface 153 of contact structures 147 (154) as shown in FIG. 22F. It isnoted that any of the contacts in FIGS. 22E and 22F need not have anaperture. Vias 156, 157 or 158 are preferably etched to a sufficientdepth such that subsequent thinning of substrate 140 of singulated die144-146 to form thinned substrate 161 after bonding die 144-146 tosurface 143 of substrate 140 reveals the vias 156, 157 and/or 158, asshown in FIG. 22G for vias 155 and contact structures 147 (154) formedas shown in FIG. 22C.

The etching of the via defined by contact structures 147 or in contactstructure 154 can be isotropic to a desired extent to form aself-aligned ledge 162 on the backside of contact structures 147 (154)as shown in FIG. 22H for via 155 of FIG. 22C to produce via 159, or asshown in FIG. 22I for vias 156 of FIG. 22D to produce via 163. Theisotropic etching can include the device region 148 underneath contactstructures 147 (154) and the substrate 140 to reveal the backside ofcontact structures 147 (154) as shown in FIG. 22H or FIG. 22I. Theisotropic etching can be achieved by modifying the etch conditions usedto etch vias 155 or vias 156. For example, if the etch conditions usedto etch vias 155 or vias 156 include a Reactive Ion Etch at lowpressure, a similar Reactive Ion Etch can be used at a higher pressure.The increase in pressure required to reveal the desired amount ofbackside of contact structures 147 and form the self-aligned ledge 162depends on a number of factors including the thickness of planarizationmaterial 151 and depth of vias 156, 157, or 158 and can be determinedexperimentally. Alternatively, the isotropic etching can includesubstrate 140 but not device region 148, resulting in a self-alignedledge 166 and residual portion 165 of device region 148 on the backsideof contact structures 147 (154) and above via 164 as shown in FIG. 22J.Similar to FIGS. 22H and 22I as described above, residual portion 165 ofdevice region 148 on the backside of contact structures 147 (154) andabove via 164 forming a self-aligned ledge 166 results with isotropicetching to a desired extent below contact structures 147 (154). Thisstructure can be formed, for example, if residual portion 165 iscomprised of an insulator, for example silicon oxide, and isotropicallyetched device region 148 and substrate 140 is comprised of asemiconductor, for example silicon.

After formation of vias, a non-selective dielectric sidewall 170 may beformed as described in the first embodiment to electrically isolatesubstrate 140 from interconnect metal that may subsequently be formed inthe vias as shown in FIG. 22K. FIG. 22K shows the example for via 163formed as shown in FIG. 22I to produce via 171 with ledges 172. Aselective dielectric sidewall 173 similar to sidewall 77 described inthe first embodiment and shown in FIG. 22L may also be formed. Afteretching vias, die 144-146 are singulated, if desired, and bonded tosurface 143 of substrate 140 with contact structures 142, and deviceregion 141. Alternatively, die 144-146 may be bonded withoutsingulation. For example, an entire wafer or die may be bonded to asubstrate with a single placement instead of separate die placements,and result in a nominally planar surface instead of a non-planar surfaceresulting from the spacing between die. Substrate 140 may also containcontact structures but not devices or a device region. Substrate 140 isthen thinned, for example with at least one of backgrinding, chemicalmechanical polishing, or etching, to leave thinned substrate die 161 andreveal vias, for example via 155 if vias are formed as described in FIG.22C and shown in FIGS. 23A-23B. Contact structures 142 can be planarwith the bond surface as shown in FIG. 23A, or recessed to the bondsurface as shown in FIG. 23B. A contact structure 142 planar with thebond surface as shown in FIG. 23A can be formed by depositing aconductive material, for example copper or nickel plating, on thesurface of substrate 140, then depositing an isolating material, overthe conductive material, followed by a chemical mechanical polish toform contact structure 142 and surface 143. The polish rate of theconductive material is preferably comparable to the polish rate of theisolating material. A comparable polish rate of the conductive materialcan be obtained with appropriate selection of conductive material,isolating material, conductive material size, shape and area coverage ofthe conductive material, and polishing parameters, including slurriesand pads as described in the fourth embodiment.

Alternatively, a contact structure 142 recessed to the bond surface asshown in FIG. 23B may be formed by deposition of an isolating material,for example, silicon oxide, followed by a chemical mechanical polish ofthe isolating material that planarizes the surface by selectivelypolishing elevated features, resulting in a thin planarized dielectricmaterial on top of contact structure 142. Alternatively, contactstructure 142 recessed to surface 143 as shown in FIG. 23B may be formedby first forming the planarized surface 143 indicated in FIG. 23A,followed by the deposition or deposition and polishing of a very thinlayer of isolating material on surface 143 shown in FIG. 23A to formsurface 143 shown in FIG. 23B. A contact structure 142 recessed to thebond surface may have an exposed surface as shown in FIG. 23C, formed,for example, by patterning and etching the planarized dielectricmaterial to expose contact structure 142 with vias 63. The bonding andthinning of die 144-146 then results in exposed surface of contactstructure 142 as shown in FIG. 23D. The exposure of contact structures142 and 147 (154), for example as shown in FIGS. 23A and 23D, arepreferred to facilitate subsequent electrical interconnection betweencontact structures 142 and 147 (154) described below. The lateral extentof exposed contact structure 142 can be less than, greater than, orequal to the lateral extent of via 155 depending on the relative size ofvia 63 and the lateral extent of via 155 etched as shown in FIG. 22C.For example, when the lateral extent of via 155 in FIG. 22C is less thanthe lateral extent of via 63 in FIG. 23C, the lateral extent of exposedcontact structure 142 is greater than the lateral extent of via 155 asshown in FIG. 23D. Alternatively, the extent of exposed contactstructures 142 may be widened after bonding, thinning, and revealingvias, for example vias 155, with an isotropic etch of exposed deviceregions 141 and 148 to contact structures 142, as shown in FIG. 23E.Alternatively, exposed contact structure 142 shown in FIG. 23C may beprotected by a thin layer during a bonding process that may otherwise bedetrimental to contact structure 142. For example, if contact structure142 is comprised of aluminum, it may be compromised by exposure toammonia-based solutions used to achieve room temperature covalentbonding. An example of such a thin layer is silicon oxide that may beformed by PECVD. Chemical mechanical polishing of the thin layer mayalso be done to maintain a desired surface 143 without removing saidthin layer from contact structure 142. The thin layer may then beremoved after bonding die 144-146 to substrate 140 and thinningsubstrate 140 to reveal the vias and form thinned die substrate 161 andis thus preferably thin, in the range of 0.05 to 0.5 microns, tosimplify removal after revealing the vias.

If thinned die substrate 161 is non-conductive, revealed contactstructures 142 and contact structures 147 (154) may be interconnectedwith the formation of conductive material overlapping contact structures142 and contact structures 147 (154). Alternatively, if thinned diesubstrate 161 is conductive, for example if thinned die substrate iscomprised of silicon, an isolating sidewall electrically isolatingthinned die substrate 161 from conductive material interconnectingcontact structures 142 and contact structures 147 (154) is preferred. Anisolating non-selective sidewall as described in earlier embodiments,for example sidewall 70 in FIG. 8A or 8B, can be formed after bonding ofdie 144-146 and subsequent thinning of die 144-146 to leave thinned diesubstrate 161 as shown in FIG. 23F for sidewall 62 when exposed contactstructure 142 is planar to surface 143, similar to that shown in FIG.23A and via 159 formed as shown in FIG. 22H, instead of sidewallformation before bonding as shown previously in FIG. 22K or FIG. 22L forvia 163 formed as shown in FIG. 22I. An isolating selective sidewallsimilar to that described in the first embodiment but formed afterbonding, thinning of die substrate, and revealing vias can also be used.As described in previous embodiments, sidewall formation is preferred toprevent undesired electrical conduction between the thinned diesubstrate and electrical interconnection between contact structures 142and contact structures 147 (154).

With contact structures 147 (154) and contact structures 142 exposed,and a sidewall on thinned die substrate 161 if preferred, an electricalinterconnection between contact structures 147 (154) and contactstructures 142 can be made by forming conductive material over exposedsurfaces of contact structures 142 and 147 (154). A typical conductivematerial is metal and typical metals are aluminum, copper, nickel, andgold. These metals can be formed with a variety of methods as describedin earlier embodiments. This formation may result in coverage of theexposed thinned die substrate 161 surface with conductive material 52 asshown in FIG. 23G. This coverage may be removed in a self-aligned mannerand without using photolithography patterning and etching by polishingthe thinned die substrate 161 surface covered with conductive material52 until conductive material 52 is removed from thinned die substrate161, as shown in FIG. 23H. When there is a residual portion 165 ofdevice region 148 with self-aligned ledge 166 as shown in FIG. 22J, astructure similar to that shown in FIG. 23I results after bonding die144-146 to substrate 140 and thinning of substrate 140 to reveal vias164 and form thinned substrate 161, when exposed contact structure 142is planar to surface 143 similar to that shown in FIG. 23A. Residualportion 165 is then preferably removed with an anisotropic etch toreposition the self-aligned ledge against the backside of contactstructures 147 (154) resulting in self-aligned ledge 167 as shown inFIG. 23J.

Conductive material can then be formed to electrically interconnectcontact structures 147 with contact structures 142 without forming anelectrical interconnection to thinned substrate 161, if preferred,similar to that described above and shown in FIGS. 23F, 23G, and 23H. Asdescribed previously, the formation of interconnect metal can be madewith one or a combination of e-beam, thermal, physical vapor deposition,chemical vapor deposition, and electroplating. Interconnect metalsformed can be one or a combination of titanium, tungsten, gold, copper,or aluminum.

After contact structures 142 and 147 (154) are electrically connectedwith conductive material, the vias can be filled and planarized with acombination of metallization, dielectric deposition, and chemicalmechanical polishing as described in previous embodiments. After viasare filled and planarized, underbump metallization, bumping, dicing, andflip-chip packaging can be done as described in previous embodiments. Itis noted that FIGS. 23F-J illustrate a surface contact 142 but thiscontact may also be recessed, as shown in FIG. 23B. Also, dies withsurface contact structures may be bonded and configured and/or connectedas illustrated in FIGS. 23F-23J. FIG. 23K illustrates the case of FIG.23H.

Also, the vias in this embodiment (e.g., FIGS. 22C-22F, 22H-L) may befilled with conductive material 168 prior to singulation so that theconductive material is exposed when the singulated portions of substrate140 are thinned. Insulating material for electrical isolation may beformed on the sidewalls of the via as needed, as discussed above. Thedie (or wafer) filled vias may then be bonded with exposed surface ofdie (or wafer) device region 148 (or die down) as described below in theninth embodiment or with the opposing surface to exposed device region148 surface (or die up) as described below in the tenth embodiment. Thebonding may be performed as described in the fourth embodiment usingcontact structures 147 and shown in the left-hand side of FIG. 23L fordie down and described in more detail below in the ninth embodiment, orin the middle structure of FIG. 23L for die up where conductive material168 is connected to contact structure 142 and described in more detailbelow in the tenth embodiment, or in the right-hand side of FIG. 23L fordie up where contact structures 179 are formed similar to the formationof contact structures 147 as described in the fourth embodiment anddescribed in more detail below in the tenth embodiment. If needed,dielectric material 169 may be formed on substrate portion 161, andpolished as needed for bonding to substrate 140. Vias may be filled witha variety or combination of conductive materials, including but notlimited to polysilicon or a variety of metals, for example tungsten,nickel or copper, deposited by a variety of methods including but notlimited to chemical vapor deposition, physical vapor deposition andelectroplating. The conductive material may be chosen to facilitate goodelectrical contact with the contact structures to which the conductivematerial is bonded, low electrical resistivity, or high thermalconductivity and may be separated from the substrate portion outside thevia or insulating material on the via sidewall by a barrier layer, forexample titanium nitride or tungsten nitride, deposited, for example, bymetal organic vapor phase deposition or physical vapor deposition, ifneeded, to prevent the conductive material from diffusing into thesubstrate portion outside the via. For example, when buildingsilicon-based ICs, where vias are etched into silicon, copper may bepreferred due to its low resistivity, but typically requires a suitablebarrier layer, typically titanium nitride or tungsten nitride between asuitable via insulating layer, typically silicon oxide to avoiddiffusion of copper into the silicon. Alternatively, other metals, forexample tungsten, may also be used, with an insulating or barrier layer,if required. Also, a material whose polishing properties areadvantageous, as discussed above, such as nickel, may be used, with aninsulating or barrier layer, if required.

An eighth embodiment is illustrated in FIGS. 24A-B. This embodiment isdistinct from the seventh embodiment in that the opposing side of die144-146, e.g., thinned die substrate, 161 is bonded to surface 143 ofsubstrate 140 after thinning the die substrate to reveal the vias. Thisresults in bonding of thinned die substrate 161 to surface 143 andexposure of vias 139 to the surface 143 as shown in FIG. 24A for vias155 formed as shown in FIG. 22C and contact structures 142 formed asshown in FIG. 23A. Thinned substrate 161, for example silicon, can bebonded directly to surface 143 of substrate 140 or a dielectric, forexample, silicon oxide, can be formed on thinned substrate 161 beforedirectly bonding to surface 143 of substrate 140. The formation ofthinned substrate 161 is preferably done at wafer-scale, prior tosingulation of die 144-146 into individual die, so that all vias, forexample vias 155 shown in FIG. 22C, on all die on a wafer are revealedsimultaneously. Die 144-146 can thus have all their vias revealedsimultaneously, or alternatively, at separate times if die 144-146originate from different wafers.

The formation of thinned substrate 161, for example from substrate 140in FIG. 22C, may compromise the mechanical integrity if the vias are notsufficiently deep. For example, a via depth of less than approximately0.1 to 0.3 mm for a thinned substrate of 200 mm diameter and comprisedof silicon is typically sufficient. This depth for vias below whichmechanical integrity is compromised will be greater for a thinnedsubstrate of greater diameter and less for a thinned substrate of lesserdiameter. This compromise in mechanical integrity can be avoided byattaching the opposing side of the exposed surface of substrate 140 to ahandle wafer 44 before the thinning of substrate 140 as shown in FIG.24B for via 155 and contact structures 147 (154) formed as shown in FIG.22C. The handle wafer 44 attachment can be done with a variety ofbonding methods including direct bonding or adhesive bonding. Afterattaching the opposing side of the exposed surface of substrate 140 to ahandle wafer 44 and thinning substrate 140 to formed thinned substrate161 and reveal via 155, the thinned substrate 161 may be used as abonding surface or a dielectric, for example, silicon oxide, may bedeposited as a bonding layer as described above. After forming thepreferred bonding surface, die 144-146 are singulated and bonded tosurface 143 of substrate 140, and the singulated portion(s) of handlewafer 44 is removed. Singulation may done with at least one of dicing orscribing. Removal of the singulated portion(s) of handle wafer 44 may bedone with at least one or a combination of grinding, chemical mechanicalpolishing, or etching.

Prior to bonding to handle wafer 44 and thinning to form thinnedsubstrate 161, contact structures 147 (154) can be formed in die 144-146as described in the seventh embodiment. However, the formation of aledge on contact structures 147 to improve the electrical connectionresistance between conductive material 52 and contact structures 147 ison the opposing side of contact structures 147 described in the seventhembodiment and shown in FIG. 23F and FIG. 23G. This ledge can thus beformed by etching the device region 148 above the contact structures 147over an extent greater than the aperture in contact structures 147 toform a via, similar to that shown for via 156 and contact structures 147in FIG. 22D.

Further, prior to bonding to handle wafer 44 and thinning to formthinned substrate 125, a sidewall can be formed in the vias. Thesidewall can be non-selective similar to that shown in FIG. 22K fornon-selective sidewall 170 and via 163 or selective similar to thatshown in FIG. 22L for selective sidewall 173 and via 163. Alternatively,a selective or non-selective sidewall may be formed after bonding die144-146 as described in earlier embodiments.

The bonding of die 144-146 to substrate 140 can be done with contactstructures 142 planar or recessed to the bond surface and exposed orprotected by a thin layer as described in the seventh embodiment. Afterbonding die 144-146, and removing singulated portion of handle wafer 44,if used, and removal of thin protective layer, if used, contactstructures 142 are exposed similar to FIG. 23A or FIG. 23D in theseventh embodiment. Conductive material is then formed to electricallyinterconnect exposed contact structures 142 and 147 (154), for examplesimilar to FIG. 23G and FIG. 23H in the seventh embodiment. Thisconductive material formation can partially or completely fill the vias.If the conductive material electrically interconnecting exposed contactstructures 142 and 147 (154) partially fills the vias, the remainingportion of the vias can be filled and planarized with a combination ofmetallization, dielectric deposition, and chemical mechanical polishingas described in previous embodiments. After vias are filled andplanarized, underbump metallization, bumping, dicing, and flip-chippackaging can be done as described in previous embodiments.

A ninth embodiment similar to the fourth embodiment with regard tobonding and electrical interconnection and similar to the seventhembodiment with regard to formation of a thru-die via prior to bondingand exposing by thinning after bonding is also possible. This embodimentstarts as described in the seventh embodiment and continues throughsingulation and bonding of die 114-116 (or wafer) with the exceptionthat the bond surfaces containing contact structures 123 and 122 areprepared, bonded and electrically interconnected as described in thefourth embodiment. After bonding, die 114-116 are thinned to expose viasin die 114-116 as described in the seventh embodiment and filled withmetal as described in earlier embodiments. The final structure wouldlook similar to FIG. 19A in the case where the via was filled andcontact structures 123 comprised an aperture.

In a variation of the ninth embodiment, the pre-bond via formation isaugmented with metal filling as described in the seventh embodiment. Forexample, vias in die 114-116 are formed prior to bonding as shown inFIGS. 22D, 22E, and 22F for vias 156, 157, and 158. If the die substrateand the portion of die device region are conductive, an electricallyinsulating sidewall is preferably formed on the conductive portion ofetched via sidewall, for example sidewall 173 in via 163 on substrate140 and device region 148 as shown in FIG. 22L. This sidewall may alsobe formed on the entire sidewall, the entire non-contact portion of thesidewall as shown in FIG. 22K, or in the bottom of the via. After thevia has been electrically isolated from the die substrate and deviceregion as appropriate, the via is filled with a conductive material, forexample metal, as shown in FIG. 10B with planarized metal structure 100or with a combination of conductive and insulating material as shown inFIG. 10C with metal lining or barrier layer 93 and dielectric 94. Thevia filling, for example with metal or metal and dielectric, can be donewith a number of techniques as described in earlier embodiments.

Alternative to etching and filling vias through the die device regionand a portion of the die substrate, the vias can be etched, or etchedand filled, into only a portion of the die substrate, or a portion ofthe die device region and a portion of the die substrate, beforeformation of devices or completion of the die device region. Forexample, as shown in FIG. 25A, vias 172 are etched into die substrate140 and through a portion of die device region 171, for example thesemiconductive portion of a device region comprised of a layer ofsemiconductor transistors and a multilevel interconnect structurecomprised of conducting material (not shown), for example metal, andinsulating material, for example silicon oxide or other suitablematerials, or where the device region would reside in the substrate. Ifportion of die device region 171 and die substrate 140 are comprised ofa conducting material, for example semiconductor materials withsufficiently low resistivity, for example silicon used in typical CMOSwafer fabrication, a sidewall is preferably formed as described earlierin this and earlier embodiments and as shown in FIG. 25B for selectivesidewall 173 that is also formed on the bottom of via 172 as describedin earlier embodiments. Furthermore, if the structure in FIG. 25A iscomprised of silicon, a very thin, for example, 5-50 nm, high qualityselective silicon dioxide sidewall can be thermally grown, facilitatingthe lateral dimensions of via 172 to be substantially less than onemicron enabling a very high areal density of vias in excess of100,000,000 per square centimeter to be fabricated. Alternatively, anon-selective sidewall can be formed on the sidewall of via 172 withoutformation on the bottom of via 172 as described in earlier embodiments.Via 172 can then be lined with a suitable barrier layer, if needed, andfilled with conductive material 174 forming, for example, a metal filledvia as described above. Via 172 may also be filled with conductivepolysilicon. Contact structures 123 may be formed in contact with thefilled vias as shown in FIG. 25D. Alternatively, further processing maybe conducted on the structure of FIG. 25C prior to formation of contactstructures 123 to complete the fabrication of die device region 148,followed by formation of contact structures 123 in the upper portion ofdie device region 148, as shown in FIG. 25E. For example a multilevelinterconnect structure may be formed comprised of conducting material,for example metal, and insulating material, for example similar to oridentical with typical CMOS wafer fabrication. Typical metals includecopper and aluminum and typical insulating materials include siliconoxide and low-k dielectrics. Contact structures 123 in die 114-116 canbe formed as described in the fourth embodiment and shown in FIG. 25E.The device region 148 may include the formation of a conducting material176 to electrically interconnect contact structures 123 with metalfilled via 174. Conducting material 176 is shown in FIG. 25E to bevertical between conductive material 174 and contact structures 123 butmay also include or entirely consist of lateral components, for exampleas provided for by the routing of interlevel metal in the fabrication oftypical integrated circuits, for example CMOS wafer fabrication. SeeFIG. 25F with conducting material 178.

Electrical connections can thus be provided from metal filled vias 174to contact structure 123 using the interconnect structure of anintegrated circuit, for example according to typical CMOS waferfabrication, effectively minimizing or eliminating the need to modifydesign rules of the interconnect structure to achieve the electricalconnections, resulting in improved scaling and leverage of existingmanufacturing capability. Note that although conducting material 176 mayinclude or consist primarily of lateral components, vias 172 do notrequire lateral components. For example, if vias 172 are in asemiconductor portion of die device region 148, for example die deviceregion 171, and the conducting material 176 consists of interlevel metaltypically used in the fabrication of integrated circuits, vias 172 aredisposed vertically from conducting material 176 and may be fabricatedwith design rules essentially independent from the fabrication ofconductive material 176 with the exception that conducting material 176be in electrical contact with metal filled via 174. Furthermore, vias172 in this example are substantially shorter than described earlier inthis embodiment, where, for example, vias 155 extend through the entireportion of die device region 148. The shorter vias 172 furtherfacilitate the lateral dimensions of via 172 to be small, for example,substantially less than one micron, enabling a very high areal densityof vias, for example, in excess of 100,000,000 per square centimeter tobe fabricated resulting in improved scaling. It is noted that in device146 an insulating sidewall film 177 and insulating surface film 180 areincluded when needed to isolate conducting material 176 and othersurface contacts.

In this variation, after bonding, post-bond thinning reveals a viafilled with metal instead of a via not filled with metal, for example asshown in the left-hand-side of FIG. 23L. In either variation, the diesubstrate portion may be entirely removed as described in the sixthembodiment. In addition, in either variation, bonding to a substratewithout a device region but with contact structures prepared asdescribed in the fourth embodiment is also possible, for example, as areplacement for a chip to package interposer substrate in a Ball GridArray IC package.

Furthermore, in either variation, the exposed surface may comprise viasfilled with metal. This surface may be suitably prepared for bondingwith electrical interconnections described in the fourth embodimentusing a combination of filler material to planarize the surface asdescribed in the first embodiment and via revealing and contactstructure formation as described in the tenth embodiment, if required.Additional die from the same or different wafers with exposed contactstructures can then be bonded to the post-bond thinned surface withrevealed metal filled vias as described in the fourth embodiment.Alternatively, under bump metallization may be formed in preparation forflip chip packaging can be implemented as described in earlierembodiments. This is illustrated in FIGS. 23M and 23N where a second dieis bonded to the first die. Many combinations are possible in connectingthe conductive material and/or contacts of one die to another die usingthe configurations described above and below. FIG. 23M shows threeexamples. where die 181 having its conductive material 168 connectedusing contact structure 179 to the conductive material 168 of the lowerdie, die 182 having contact 147(154) connected to contact 147 andconductive material 168 of the lower die, and die 183 having contact 147and conductive material 168 connected to contact 147 and conductivematerial 168 of the lower die.

In FIG. 23N, the left-hand structure has two die bonded in the die-downconfiguration. The middle structure has a die with contact structure147(154) bonded to a substrate 149, such as an interposer, having acontact structure 142. Contact structure 147 (154) and conductivematerial 168 are connected through conductive material 187 formed afterbonding. The right-hand structure has conductive material 187 connectingconductive material 168 in substrate 149 and contact structure 154.

As mentioned above, the method according to the invention may be appliedto wafer to wafer bonding. FIG. 23O illustrates an upper substrate 140with multiple contact structures 147 and conductive material 168, likethe die on the left-hand side of FIG. 23L, is bonded to a lowersubstrate 140 making respective connections with contact structures 142.Die or another wafer may be bonded to wafer 149, using the methods andconfigurations described above and below. Any desired number of wafersand dies may be bonded and interconnected together.

A tenth embodiment similar to the ninth embodiment with regard tobonding and electrical interconnection and similar to the eighthembodiment with regard to orientation of the die 144-146 bond surfaceand optional use of a handle wafer is also possible, and is shown inFIG. 26A. This embodiment starts as described in the ninth embodimentwhere vias are etched, isolated if required, and filled with conductivematerial, for example as shown in FIG. 25C. As mentioned above, vias maybe filled with a variety of conductive materials, including but notlimited to polysilicon or a variety of metals, for example tungsten orcopper deposited by a variety of methods including but not limited tochemical vapor deposition and electroplating, using insulating andbarrier layers as required. The die (or wafer) substrate, for example140 in FIG. 25F, is then thinned to reveal vias filled with conductivematerial, for example 174 in FIG. 25F, with optional use of a handlewafer as described in the eighth embodiment. The revealing of the viascan be done with a combination of backgrinding, CMP, and etching. Therevealing preferably results in a planar surface but alternatively, mayresult in nonplanar surface due to selectivity of the CMP or etching ofthe substrate. For example, silicon may be removed during the CMPprocess at a lower rate than copper, resulting in a conductive viarecessed or dished below the silicon substrate surface as described inthe fourth embodiment. Alternatively, the vias may be revealed or therevealed vias may be etched with a selective etch that preferentiallyetches the substrate versus the conductive via resulting in a conductivevia extended above the silicon substrate surface. For example, siliconmay be etched preferentially versus a copper or tungsten filled via witha SF6-based reactive ion etch. If revealing of a conductive filled viaresults in a suitable bondable surface as described in the fourthembodiment, die may be singulated and bonded as described in the eighthembodiment.

If revealing of a conductive filled via does not result in a suitablebondable surface as described in the fourth embodiment, contactstructures may be formed to form a suitable bondable surface asdescribed in the fourth embodiment. For example, if exposed conductivevia fill is below the bonding surface, contact structures 179 may beformed on conductive material 174 in a manner similar to that describedin the fourth embodiment. This formation may include the deposition ofcontact structures and a dielectric, for example silicon oxide, followedby polishing, to result in a bonding surface that is suitably planar andelectrically insulating, with the exception of the contact structures.This is illustrated in FIG. 26B having contact structures 179 formed incontact with conductive material 174 and having dielectric film 169,such as PECVD silicon oxide.

Alternatively, the process may include the depositing and polishing ofcontact structures, with or without a dielectric, to result in a bondingsurface that is suitably planar with contact structures and comprised ofsubstrate, for example, substrate 140 in FIG. 25F.

Further alternatively, if exposed conductive fill is above the bondingsurface, contact structures may also be formed on conductive material174 in a manner similar to that described in the fourth embodiment. Thisformation may include the deposition and polishing of contact structuresand a dielectric, for example silicon oxide, to result in a bondingsurface that is suitably planar and electrically insulating, with theexception of the contact structures 179. Contact structures 179 may beformed of a comparable, smaller, or larger lateral dimension thanconductive material 174.

The die are then singulated and bonded as described in the eighthembodiment. Die 144-146 are thus bonded to substrate 140 with pre-bondvias formed and filled as described in the ninth embodiment, and bondsurfaces, containing contact structures, if required, are prepared,bonded and electrically interconnected as described in the fourthembodiment. After bonding of die 144-146 to substrate 140, die 144-146do not need to be electrically interconnected to contact structures 142and the exposed surfaces of die 114-116 are accessible for under bumpmetallization in preparation for flip chip packaging as described inprevious embodiments.

In embodiment ten, vias can be formed either through the entire deviceregion 148 or a semiconductor portion of device region 148 as describedin embodiment nine. As in the ninth embodiment, forming the vias in asemiconductor region of device region 148 avoids a deeper and wider viaby forming vias before the device region is completed, which improvesdevice density and reduces the portion of semiconductor consumed as aresult of via formation, resulting in improved scaling. Furthermore, thedie substrate portion may be entirely removed as described in the sixthembodiment. Furthermore, the exposed surface may comprise contactstructures. This surface may be suitably prepared for bonding withelectrical interconnections described in the fourth embodiment using,filler material to planarize the surface as described in the firstembodiment, if required. Additional die from the same or differentwafers with exposed metal filled vias can then be bonded to thepost-bond surface with suitable contact structures as described in thefourth embodiment. Alternatively, under bump metallization may be formedin preparation for flip chip packaging can be implemented as describedin earlier embodiments. Also, embodiment ten may also be carried out tostack multiple dies, similar to FIG. 23M or in wafer-to-wafer format,similar to FIG. 23N.

The desirable features of the invention convey to vertical stacking andinterconnection configurations. For example, die may be bonded IC-sidedown or IC-side up. In addition, alternative to the die-to-wafer format,a wafer-to-wafer format is also possible with the upper wafer, eitherIC-side up or down, bonded to the lower wafer IC-side up. Furthermore,these die-to-wafer and wafer-to-wafer formats can also be used with ICsfabricated using substrates that do not require the substrate for ICfunctionality. For example, ICs fabricated using silicon-on-insulator(SOI) substrates or non-silicon substrates, for example III/V materials,SiC, and sapphire, may not require the existence of the substrate for ICfunctionality. In these circumstances, the entire portion of thesubstrate that is not used for transistor fabrication may be removed, tominimize the via etching required to form vertical electricalinterconnection.

Although substrates are shown comprised of a device region, a substratewithout a device region but with contact structures is also possible,for example, as a replacement for a chip to package interposer substratein a Ball Grid Array IC package. Also, the die are shown with devicesbut other dies or elements not having a device or devices but havingcontact structures may be bonded to a substrate using the methodsaccording to the invention.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed:
 1. A method of bonding a first element with a secondelement, the method comprising: forming a first contact structure in thefirst element; forming a second contact structure in the second element;contacting a first non-metallic region of the first element with asecond non-metallic region of the second element, wherein a gap isdisposed between the first contact structure and the second contactstructure; directly bonding the first non-metallic region of the firstelement to the second non-metallic region of the second element; andheating the first element and the second element to form a direct bondbetween the first contact structure and the second contact structurewithout melting or reflowing the first contact structure or the secondcontact structure.
 2. The method of claim 1, wherein forming the firstcontact structure comprises positioning an upper surface of the firstcontact structure below an upper surface of the first non-metallicregion.
 3. The method of claim 2, wherein forming the first contactstructure comprises positioning the upper surface of the first contactstructure below the upper surface of the first non-metallic region byless than 20 nm.
 4. The method of claim 3, wherein forming the firstcontact structure comprises positioning the upper surface of the firstcontact structure below the upper surface of the first non-metallicregion by less than 10 nm.
 5. The method of claim 2, wherein forming thesecond contact structure comprises positioning an upper surface of thesecond contact structure below an upper surface of the secondnon-metallic region.
 6. The method of claim 5, wherein forming thesecond contact structure comprises positioning the upper surface of thesecond contact structure below the upper surface of the secondnon-metallic region by less than 20 nm.
 7. The method of claim 2,wherein forming the second contact structure comprises positioning anupper surface of the second contact structure to extend above an uppersurface of the second non-metallic region.
 8. The method of claim 1,further comprising forming a via in the first element exposed to atleast the first contact structure.
 9. The method of claim 8, furthercomprising forming a conductive material in the via and connected to atleast the first contact structure.
 10. The method of claim 1, whereinheating the first and second elements comprises heating to a temperatureless than 400° C. to increase the pressure between the first and secondcontact structures.
 11. The method of claim 1, wherein forming the firstand second contact structures comprises forming from a metal selectedfrom copper, tungsten, nickel, gold or alloys thereof.
 12. The method ofclaim 1, further comprising etching a surface of at least one of thefirst and second elements adjacent to respective first and secondcontact structures prior to bonding.
 13. The method of claim 1, wherein:forming the first contact structure comprises forming from a firstmetal; and forming the second contact structure comprises forming from asecond metal different from the first metal.
 14. The method of claim 1,wherein each of the first and second non-metallic regions comprises oneof an oxide and a nitride material.
 15. A method of bonding a firstelement with a second element, the method comprising: forming a firstcontact structure in the first element; forming a second contactstructure in the second element; contacting a first non-metallic regionof the first element with a second non-metallic region of the secondelement, wherein a gap is disposed between the first contact structureand the second contact structure; directly bonding the firstnon-metallic region of the first element to the second non-metallicregion of the second element; and expanding the first and second contactstructures to cause the first contact structure to contact and directlybond with the second contact structure without melting or reflowing thefirst contact structure or the second contact structure.
 16. The methodof claim 15, wherein forming the first contact structure comprisesproviding an upper surface of the first contact structure below an uppersurface of the first non-metallic region.
 17. The method of claim 16,wherein forming the first contact structure comprises providing theupper surface of the first contact structure below the upper surface ofthe first non-metallic region by less than 20 nm.
 18. The method ofclaim 17, wherein forming the first contact structure comprisesproviding the upper surface of the first contact structure below theupper surface of the first non-metallic region by less than 10 nm. 19.The method of claim 15, wherein expanding the first and second contactstructures comprises heating the first and second elements.
 20. Themethod of claim 15, wherein, after expanding the first and secondcontact structures, a perimeter of the first contact structure is withina perimeter of the second contact structure.
 21. The method of claim 15,wherein forming the first and second contact structures comprisesforming from a metal selected from copper, tungsten, nickel, gold oralloys thereof.
 22. The method of claim 15, wherein expanding the firstand second contact structures comprises increasing an internal pressurebetween the first and second contact structures.